Separator for non-aqueous secondary battery and non-aqueous secondary battery

ABSTRACT

Provided is a separator for a non-aqueous secondary battery, including: a porous substrate, and a heat resistant porous layer that is provided on one side or both sides of the porous substrate, that is an aggregate of resin particles and an inorganic filler, and that satisfies the following expression (1). In expression (1), Vf is a volume proportion (% by volume) of the inorganic filler in the heat resistant porous layer, and CPVC is a critical pigment volume concentration (% by volume) of the inorganic filler. Also provided is a separator for a non-aqueous secondary battery, including: a porous substrate, a heat resistant porous layer that is provided on one side or both sides of the porous substrate, that includes a resin and an filler, and that satisfies the following expression (2), and an adhesive porous layer that is provided on both sides of a stacked body of the porous substrate and the heat resistant porous layer, and that includes an adhesive resin. In expression (2), Vf is a volume proportion (% by volume) of the filler in the heat resistant porous layer, and CPVC is a critical pigment volume concentration (% by volume) of the filler.
 
0.65≤ Vf /CPVC≤0.99  expression (1)
 
0.40≤ Vf /CPVC≤0.99  expression (2)

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2013/079032 filed Oct. 25, 2013 (claiming priority based onJapanese Patent Application Nos. 2012-262515 filed on Nov. 30, 2012,2012-262516 filed on Nov. 30, 2012, 2013-056710 filed on Mar. 19, 2013,2013-056712 filed on Mar. 19, 2013 and 2013-123873 filed on Jun. 12,2013), the contents of which are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

The present invention relates to a separator for a non-aqueous secondarybattery and a non-aqueous secondary battery.

BACKGROUND ART

Non-aqueous secondary batteries, typified by lithium ion secondarybatteries, have been widely used as main power sources for portableelectronic devices such as cellular phones or notebook computers.Further, application of non-aqueous secondary batteries has beenexpanded to main power sources for electric automobiles or hybrid cars,and to systems for storing nighttime electricity. Along with thepopularization of non-aqueous secondary batteries, securing stablebattery performance and safety has become a challenge.

Separators play an important role in securing safety for a non-aqueoussecondary battery. Particularly from the viewpoint of a shutdownfunction, polyolefin porous membranes having polyolefin as a maincomponent are currently used.

However, a separator which is composed only of a polyolefin porousmembrane may be melted in its entirety (a so-called meltdown) when theseparator is exposed to a temperature higher than the temperature atwhich a shutdown function occurs.

Since polyolefin is poorly adhesive to other resins or other materials,adhesion between a polyolefin porous membrane and an electrode is notsufficient, which has caused deterioration in battery capacity ordeterioration in cycle characteristics in some cases.

Accordingly, a suggestion has been made to provide a porous layercontaining a resin and a filler on one side or both sides of apolyolefin porous membrane for the purpose of improving the heatresistance of a separator or improving the adhesion between an electrodeand a separator (see, for example, Patent Documents 1 to 9).

Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No.2000-030686

Patent Document 2: Japanese National-Phase Publication (JP-A) No.2012-529742

Patent Document 3: JP-A No. 2011-171290

Patent Document 4: JP-A No. 2010-065088

Patent Document 5: JP-A No. 2000-057846

Patent Document 6: JP-A No. 2009-021265

Patent Document 7: JP-A No. 2006-286531

Patent Document 8: JP-A No. 2009-187702

Patent Document 9: JP-A No. 2002-141042

SUMMARY OF INVENTION Technical Problem

Although a variety of separators for non-aqueous secondary batterieshave hitherto been proposed, further improvement in performance isdemanded; for example, separators excellent both in ion permeability andthermal dimensional stability or separators having heat resistance,adhesion to an electrode and ion permeability in good balance aredemanded.

The present invention has been made under the above-mentionedcircumstances.

An object of a first embodiment of the present invention is to provide aseparator for a non-aqueous secondary battery having excellent ionpermeability and excellent thermal dimensional stability, and anon-aqueous secondary battery having excellent battery characteristicsand high safety, and the first embodiment of the present invention aimsto attain the object.

An object of a second embodiment of the present invention is to providea separator for a non-aqueous secondary battery having heat resistance,adhesion to an electrode and ion permeability in a good balance, and anon-aqueous secondary battery having excellent battery characteristicsand high safety, and the second embodiment of the present invention aimsto attain the object.

Solution to Problem

The first embodiment of the present invention employs the followingconfiguration in order to solve the problem.

<1> A separator for a non-aqueous secondary battery, including:

a porous substrate, and

a heat resistant porous layer that is provided on one side or both sidesof the porous substrate, that is an aggregate of resin particles and aninorganic filler, and that satisfies the following expression (1).0.65≤Vf/CPVC≤0.99  expression (1)

In expression (1), Vf is a volume proportion (% by volume) of theinorganic filler in the heat resistant porous layer, and CPVC is acritical pigment volume concentration (% by volume) of the inorganicfiller.

<2> The separator for a non-aqueous secondary battery according to <1>,wherein the heat resistant porous layer has a porosity of from 40% to70%.

<3> The separator for a non-aqueous secondary battery according to <1>,wherein a product, of the porosity of the heat resistant porous layerand Vf/CPVC, is from 40% to 60%.

<4> The separator for a non-aqueous secondary battery according to anyone of <1> to <3>, wherein a content of the inorganic filler in the heatresistant porous layer is from 2.0 g/m² to 20.0 g/m².

<5> The separator for a non-aqueous secondary battery according to anyone of <1> to <4>, wherein the critical pigment volume concentration ofthe inorganic filler is from 20% by volume to 70% by volume.

<6> The separator for a non-aqueous secondary battery according to anyone of <1> to <5>, wherein:

the porous substrate includes a thermoplastic resin, and

in a case in which the separator for a non-aqueous secondary battery isheated at a rate of temperature increase of 5° C./min. to a flowelongation deformation temperature of the thermoplastic resin, theseparator for a non-aqueous secondary battery exhibits a thermaldimensional change ratio in a longitudinal direction of 3% or less and athermal dimensional change ratio in a width direction of 3% or less.

<7> The separator for a non-aqueous secondary battery according to anyone of <1> to <6>, wherein in a case in which the separator for anon-aqueous secondary battery is subjected to a heat treatment at 150°C. for 30 minutes are 3% or less, the separator for a non-aqueoussecondary battery exhibits a thermal shrinkage ratio in a longitudinaldirection of 3% or less and a thermal shrinkage ratio in a widthdirection of 3% or less.

<8> The separator for a non-aqueous secondary battery according to anyone of <1> to <7>, wherein the resin particles are resin particlesinclude a polyvinylidene fluoride resin.

<9> The separator for a non-aqueous secondary battery according to anyone of <1> to <8>, wherein the inorganic filler is magnesium hydroxideor magnesium oxide.

<10> The separator for a non-aqueous secondary battery according to anyone of <1> to <9>, wherein the proportion of the inorganic filler withrespect to the total amount of the resin particles and the inorganicfiller is from 65% by mass to 99% by mass.

<11> The separator for a non-aqueous secondary battery according to anyone of <1> to <10>, wherein a content of the resin particles in the heatresistant porous layer is from 0.5% by mass to 30% by mass.

<12> The separator for a non-aqueous secondary battery according to anyone of <1> to <11>, wherein the heat resistant porous layer furtherincludes a thickener.

<13> A non-aqueous secondary battery including a positive electrode, anegative electrode, and the separator for a non-aqueous secondarybattery according to any one of <1> to <12>, which is disposed betweenthe positive electrode and the negative electrode,

wherein, in the non-aqueous secondary battery, electromotive force isobtained by lithium doping/dedoping.

The second embodiment of the present invention employs the followingconfiguration in order to solve the problem.

<101> A separator for a non-aqueous secondary battery, including:

a porous substrate,

a heat resistant porous layer that is provided on one side or both sidesof the porous substrate, that includes a resin and an filler and thatsatisfies the following expression (2), and

an adhesive porous layer that is provided on both sides of a stackedbody of the porous substrate and the heat resistant porous layer, andthat includes an adhesive resin.0.40≤Vf/CPVC≤0.99  expression (2)

In expression (2), Vf is a volume proportion (% by volume) of the fillerin the heat resistant porous layer, and CPVC is a critical pigmentvolume concentration (% by volume) of the filler.

<102> The separator for a non-aqueous secondary battery according to<101>, wherein an average of a porosity of the heat resistant porouslayer and a porosity of the adhesive porous layer is from 30% to 70%.

<103> The separator for a non-aqueous secondary battery according to<101> or <102>, wherein, in the heat resistant porous layer, aproportion of the filler with respect to a total amount of the resin andthe filler is from 50% by mass to 98% by mass.

<104> The separator for a non-aqueous secondary battery according to anyone of <101> to <103>, wherein the critical pigment volume concentrationof the filler is from 20% by volume to 80% by volume.

<105> The separator for a non-aqueous secondary battery according to anyone of <101> to <104>, wherein the peel strength between the heatresistant porous layer and the adhesive porous layer is 0.05 N/cm ormore.

<106> The separator for a non-aqueous secondary battery according to anyone of <101> to <105>, wherein as the resin is resin particles includinga polyvinylidene fluoride resin, the filler is an inorganic filler, andthe heat resistant porous layer is an aggregate of the resin particlesand the inorganic filler.

<107> The separator for a non-aqueous secondary battery according to anyone of <101> to <106>, wherein the filler is magnesium hydroxide ormagnesium oxide.

<108> The separator for a non-aqueous secondary battery according to anyone of <101> to <107>, wherein the porous substrate includes athermoplastic resin.

<109> The separator for a non-aqueous secondary battery according to anyone of <101> to <108>, wherein a content of the resin in the heatresistant porous layer is from 1% by mass to 50% by mass.

<110> The separator for a non-aqueous secondary battery according to anyone of <101> to <109>, wherein the adhesive porous layer includes apolyvinylidene fluoride resin.

<111> The separator for a non-aqueous secondary battery according to anyone of <101> to <110>, wherein the heat resistant porous layer furtherincludes a thickener.

<112> A non-aqueous secondary battery including a positive electrode, anegative electrode, and the separator for a non-aqueous secondarybattery according to any one of <101> to <111>, which is disposedbetween the positive electrode and the negative electrode,

wherein, in the non-aqueous secondary battery, electromotive force isobtained by lithium doping/dedoping.

Advantageous Effects of Invention

According to the first embodiment of the present invention, a separatorfor a non-aqueous secondary battery having excellent ion permeabilityand excellent thermal dimensional stability, and a non-aqueous secondarybattery having excellent battery characteristics and high safety areprovided.

According to the second embodiment of the present invention, a separatorfor a non-aqueous secondary battery having heat resistance, adhesion toelectrodes, and ion permeability in good balance, and a non-aqueoussecondary battery having excellent battery characteristics and highsafety are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross-sectional view of one embodiment of thepresent invention.

FIG. 2 shows a schematic cross-sectional view of another embodiment ofthe present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described. Itis noted that such descriptions and Examples exemplify the presentinvention, and do not limit the scope of the present invention.

Numerical ranges indicated by using “to” refer to ranges includingvalues before and after “to” as the minimum value and the maximum value,respectively.

The term “process” herein not only means an independent process but alsoencompasses in its scope a process which is not clearly distinguishedfrom other processes as long as a desired effect thereof is attained.

The term “(meth)acrylic” herein means “acrylic” or “methacrylic”.

Herein, with respect to a separator for a non-aqueous secondary battery,a “longitudinal direction” means a direction of the longer side of aseparator manufactured in a long shape, and a “width direction” means adirection orthogonal to the longitudinal direction of a separator. The“longitudinal direction” is also referred to as “MD direction”, and the“width direction” is also referred to as “TD direction”.

Herein the “heat resistance” means characteristics in which melting ordecomposition does not occur in a temperature range of 200° C. or lower.

Hereinafter, two forms of a separator for a non-aqueous secondarybattery (hereinafter, also referred to as “separator”) according to thepresent invention are described.

<Separator for Non-Aqueous Secondary Battery According to FirstEmbodiment>

A separator according to a first embodiment includes a porous substrateand a heat resistant porous layer provided on one side or both sides ofthe porous substrate. The heat resistant porous layer is an aggregate ofresin particles and an inorganic filler, and satisfies the followingexpression (1).0.65≤Vf/CPVC≤0.99  Expression (1)

In expression (1), Vf is the volume proportion (% by volume) of theinorganic filler in the heat resistant porous layer, and CPVC is thecritical pigment volume concentration (% by volume) of the inorganicfiller.

The heat resistant porous layer which the separator according to thefirst embodiment includes is an aggregate that is in a layer shape andis formed by coupling plural resin particles and plural inorganic fillerparticles, and, with the heat resistant porous layer, surface pores ofthe porous substrate are less likely to be occluded, whereby theseparator according to the first embodiment has an excellent ionpermeability.

In the separator according to the first embodiment, with regard to theinorganic filler contained in the heat resistant porous layer, the ratioVf/CPVC of the volume proportion (% by volume) of the inorganic fillerto the CPVC (critical pigment volume concentration) (% by volume) of theinorganic filler is from 0.65 to 0.99. When the Vf/CPVC is 0.65 orlarger, both the ion permeability and the thermal dimensional stabilityof the separator are excellent. From this point of view, Vf/CPVC ispreferably 0.70 or larger, and more preferably 0.80 or larger. On theother hand, when the Vf/CPVC is 0.99 or less, the inorganic filler isless likely to fall off from the heat resistant porous layer, and theheat resistant porous layer is less likely to be peeled off from theporous substrate. Accordingly, the thermal dimensional stability can bemaintained. From this point of view, the Vf/CPVC is preferably 0.985 orless, and more preferably 0.98 or less.

The CPVC (critical pigment volume concentration) of the inorganic filleris a physical property obtained by measuring the linseed oil absorptionamount per unit mass in accordance with JIS K-5101-13-1 (2004) andcalculating using the following formula.CPVC (% by volume) of inorganic filler=linseed oil absorption amount perunit mass (ml/g)×specific gravity (g/cm³) of inorganic filler×100

The CPVC of the inorganic filler is a physical property determined bysynthesizing factors such as the material properties, particle size,particle size distribution, shape and the like of the inorganic filler,and can be controlled by adjusting each of these factors. For example,the CPVC can be adjusted by pulverizing the inorganic filler or addingthereto an inorganic filler having a different particle size.

The volume proportion Vf of the inorganic filler in the heat resistantporous layer is calculated by the following formula.volume proportion Vf (% by volume) of inorganic filler=volume per unitarea (cm³/m²) of inorganic filler÷volume per unit area (cm³/m²) of heatresistant porous layer×100

The volume per unit area (cm³/m²) of the inorganic filler is determinedby dividing the weight per unit area (g/m²) of the inorganic filler bythe specific gravity (g/cm³) of the inorganic filler. The volume perunit area (cm³/m²) of the heat resistant porous layer is determined bythe product of the thickness of the heat resistant porous layer and theunit area. The weight per unit area (g/m²) of the inorganic filler mayalso be determined by the weight per unit area (basis weight, g/m²) ofthe heat resistant porous layer and the composition of the heatresistant porous layer, or may be determined by TGA (thermogravimetricanalysis).

The volume proportion Vf of the inorganic filler in the heat resistantporous layer can be controlled by the composition or porosity of theheat resistant porous layer.

Hereinafter, components of the separator according to the firstembodiment, and ingredients contained in each of the components aredescribed.

[Porous Substrate]

In the invention, the term “porous substrate” means a substrate havingpores or voids inside. Examples of such a substrate include amicroporous membrane; a porous sheet formed of a fibrous material, suchas nonwoven fabric or a paper-like sheet; and the like. Particularlyfrom the viewpoints of thinning of a separator and high strength, amicroporous membrane is preferable. The “microporous membrane” means amembrane that has a large number of micropores inside, and has astructure in which these micropores are joined, to allow gas or liquidto pass therethrough from one side to the other side.

The material used as a component of the porous substrate may be anorganic material or an inorganic material as long as the material is anelectrically insulating material.

The material used as a component of the porous substrate is preferably athermoplastic resin from the viewpoint of imparting a shutdown functionto the porous substrate. The term “shutdown function” refers to thefollowing function. Namely, in a case in which the battery temperatureincreases, the thermoplastic resin melts and blocks the pores of theporous substrate, thereby blocking migration of ions, to prevent thermalrunaway of the battery. Examples of the thermoplastic resin includepolyesters such as polyethylene terephthalate; and polyolefins such aspolyethylene and polypropylene. As the thermoplastic resin, a resinhaving a flow elongation deformation temperature of lower than 200° C.is preferable from the viewpoint of imparting a shutdown function.

In the present invention, the flow elongation deformation temperature ofthe thermoplastic resin is a temperature at which the elongationpercentage (=elongation amount÷initial sample length×100) is 15% whenthe temperature of a sample is increased at a constant rate while aconstant tensile force is applied thereto to measure the elongation ofthe sample. Specifically, the flow elongation deformation temperature isa temperature determined by the following method.

A porous substrate formed of a thermoplastic resin is cut into a 3 mm(TD direction)×16 mm (MD direction) piece and a 3 mm (MD direction)×16mm (TD direction) piece. A sample is placed into a TMA measurementdevice, a TMA (thermomechanical analysis) is performed at atemperature-rising rate of 5° C./min. while applying a load of 19.6 mNin the longitudinal direction of the sample, and a TMA chart is preparedby plotting the temperature along the horizontal axis and the samplelength along the vertical axis for each of the MD direction and the TDdirection. For each of the MD direction and the TD direction, thetemperature at which the elongation percentage of the sample reaches 15%is determined from the TMA chart, and the average of the temperaturesfor the MD direction and the TD direction is calculated, therebyobtaining the flow elongation deformation temperature of thethermoplastic resin that is a component of the porous substrate.

As the porous substrate, a microporous membrane (referred to as“polyolefin microporous membrane”) including polyolefin is preferable.As the polyolefin microporous membrane, a polyolefin microporousmembrane which has sufficient mechanical characteristic and ionpermeability may be selected from polyolefin microporous membranes whichhave been applied to a conventional separator for a non-aqueoussecondary battery.

From the viewpoint of exhibiting the shutdown function, the polyolefinmicroporous membrane preferably includes polyethylene, and the contentof polyethylene is preferably 95% by mass or larger.

From the viewpoint of imparting heat resistance to such a degree thatthe membrane does not easily break when exposed to high temperatures, apolyolefin microporous membrane including polyethylene and polypropyleneis preferable. An example of such a polyolefin microporous membrane is amicroporous membrane in which polyethylene and polypropylene are presentas a mixture in one layer. In such a microporous membrane, it ispreferable that polyethylene is contained in an amount of 95% by mass ormore and polypropylene is contained in an amount of 5% by mass or less,from the viewpoint of achieving both the shutdown function and heatresistance. From the viewpoint of achieving both the shutdown functionand heat resistance, a polyolefin microporous membrane having amulti-layer structure of two or more layers, in which at least one layerincludes polyethylene and at least one layer includes propylene, is alsopreferable.

It is preferable that the polyolefin contained in the polyolefinmicroporous membrane has a weight average molecular weight of from100,000 to 5,000,000. When the weight average molecular weight is100,000 or more, sufficient mechanical characteristics can be ensured.When the weight average molecular weight is 5,000,000 or less, theshutdown characteristics are favorable, and it is easy to form amembrane.

The polyolefin microporous membrane can be manufactured, for example, bythe following method. Namely, the polyolefin microporous membrane can bemanufactured by a method in which a molten polyolefin resin is extrudedthrough a T-die to form a sheet, the sheet is subjected to acrystallization treatment, followed by stretching, and further issubjected to a heat treatment, thereby obtaining a microporous membrane.Alternatively, the polyolefin microporous membrane can be manufacturedby a method in which a polyolefin resin melted together with aplasticizer such as liquid paraffin is extruded through a T-die,followed by cooling, to form a sheet, the sheet is stretched, theplasticizer is extracted from the sheet, and the sheet is subjected to aheat treatment, thereby obtaining a microporous membrane.

Examples of the porous sheet formed of a fibrous material include aporous sheet formed of a nonwoven fabric formed of fibrous material of athermoplastic resin, a paper, or the like.

From the viewpoint of obtaining favorable mechanical characteristics andinternal resistance, the thickness of the porous substrate is preferablyfrom 3 μm to 25 μm, and more preferably from 5 μm to 25 μm.

From the viewpoints of preventing a short circuit in a battery andobtaining ion permeability, the Gurley value (JIS P8117(2009)) of theporous substrate is preferably from 50 sec/100 cc to 800 sec/100 cc, andmore preferably from 50 sec/100 cc to 400 sec/100 cc.

From the viewpoint of obtaining an appropriate film resistance andshutdown function, the porosity of the porous substrate is preferablyfrom 20% to 60%.

From the viewpoint of improving the production yield, the piercingstrength of the porous substrate is preferably 300 g or more.

For the purpose of improving wettability with a coating liquid forforming a heat resistant porous layer or an adhesive porous layer, thesurface of the porous substrate may be subjected to a corona treatment,a plasma treatment, a flame treatment, an ultraviolet irradiationtreatment, or the like.

[Heat Resistant Porous Layer]

The separator according to the first embodiment includes a heatresistant porous layer on one side or both sides of the poroussubstrate. When the separator has a heat resistant porous layer only onone side of the porous substrate, the thickness of the whole separatorcan be minimized, thereby contributing to improvement of the batterycapacity, and favorable ion permeability can be easily obtained due to asmall number of layers. On the other hand, when the heat resistantporous layer is provided on both sides of the porous substrate, the heatresistance of the separator is more excellent, and safety of a batterycan be improved. When the heat resistant porous layer is provided onboth sides of the porous substrate, a curl is less likely to begenerated on the separator.

In the first embodiment, the heat resistant porous layer is an aggregateof resin particles and inorganic fillers. In other words, plural resinparticles and plural inorganic filler particles are joined to form alayered aggregate, and the aggregate is fixed on the surface of theporous substrate via at least part of the resin particles. The aggregatehas a porous structure in a layer shape as a whole, and gas or liquidcan pass from one side to the other side. Resin particles in theaggregate are preferably joined with each other and with the inorganicfiller. The resin particle retaining its particle shape can be confirmedby observing the surface of the heat resistant porous layer with an SEM(scanning electron microscope).

—Resin Particles—

As the resin particle, a particle that is stable with respect to anelectrolyte, that is electrochemically stable, and that has a functionof joining an inorganic filler is preferable. Specific examples of theresin particle include a particle including a resin such as apolyvinylidene fluoride resin, fluoro rubber, styrene-butadiene rubber,ethylene-acrylate copolymer, ethylene-acrylic acid copolymer,polyethylene, ethylene-vinyl acetate copolymer, and a cross-linkedacrylic resin. Among them, a particle including a polyvinylidenefluoride resin is preferable from the viewpoint that the particle has anexcellent oxidation resistance.

Examples of the polyvinylidene fluoride resin include homopolymers ofvinylidene fluoride (polyvinylidene fluoride), and copolymers ofvinylidene fluoride and another monomer (polyvinylidene fluoridecopolymer), a mixture of polyvinylidene fluoride and an acrylic polymer,and a mixture of a polyvinylidene fluoride copolymer and an acrylicpolymer.

Examples of the monomer that is copolymerizable with vinylidene fluorideinclude vinyl fluoride, chlorotrifluoroethylene, tetrafluoroethylene,hexafluoropropylene, trifluoroethylene, trichloroethylene,trifluoroperfluoropropylether, ethylene, (meth)acrylic acid, methyl(meth)acrylate, (meth)acrylic acid ester, vinyl acetate, vinyl chloride,and acrylonitrile. These monomers may be used singly or in combinationof two or more thereof.

The weight-average molecular weight of each polyvinylidene fluoride anda polyvinylidene fluoride copolymer, as a component of the resinparticle, is preferably from 1,000 to 5,000,000, more preferably from10,000 to 2,000,000, and further preferably from 50,000 to 1,000,000.Each of polyvinylidene fluoride and a polyvinylidene fluoride copolymercan be synthesized by emulsion polymerization or suspensionpolymerization.

Examples of acrylic polymer as a component of the resin particle includea poly(meth)acrylic acid, a poly(meth)acrylic acid salt, apoly(meth)acrylic acid ester, a cross-linked poly(meth)acrylic acid, across-linked poly(meth)acrylate, and a cross-linked poly(meth)acrylicacid ester, and a modified acrylic polymer may be used. These acrylicpolymers may be used singly or in combination of two or more thereof.

As a resin that is a component of the resin particle, it is preferableto use polyvinylidene fluoride, a copolymer of vinylidene fluoride andtetrafluoroethylene, a copolymer of vinylidene fluoride andhexafluoropropylene, a copolymer of vinylidene fluoride andtrifluoroethylene, a mixture of polyvinylidene fluoride and an acrylicpolymer, or a mixture of a polyvinylidene fluoride copolymer and anacrylic polymer. From the viewpoint of obtaining mechanical strengthwith which a battery can withstand an applied pressure or heat duringits manufacture, the polyvinylidene fluoride copolymer is preferably acopolymer that includes structural units derived from vinylidenefluoride in an amount of 50 mole % or more.

From the viewpoint of oxidation resistance, each of the mixture ofpolyvinylidene fluoride and an acrylic polymer and the mixture of apolyvinylidene fluoride copolymer and an acrylic polymer, as a componentof the resin particle, preferably include polyvinylidene fluoride or apolyvinylidene fluoride copolymer in an amount of 20% by mass or more.

From the viewpoint of handling properties or manufacturability, thevolume average particle diameter of the resin particles is preferablyfrom 0.01 μm to 1 μm, more preferably from 0.02 μm to 1 μm, and furtherpreferably from 0.05 μm to 1 μm.

The content of the resin particles in the heat resistant porous layer ispreferably from 0.5% by mass to 30% by mass. When the content of theresin particle is 0.5% by mass or more, an inorganic filler is lesslikely to fall off from the heat resistant porous layer, and the heatresistant porous layer is less likely to be peeled off from the poroussubstrate. From this point of view, the content of the resin particle ismore preferably 1% by mass or more, further preferably 3% by mass ormore, and still further preferably 5% by mass or more. On the otherhand, when the content of the resin particle is 30% by mass or less, thethermal dimensional stability and ion permeability of the separator aremore excellent. From this point of view, the content of the resinparticle is more preferably 25% by mass or less, and further preferably20% by mass or less.

—Inorganic Filler—

As the inorganic filler, an inorganic filler which is stable to enelectrolyte and which is electrochemically stable is preferable.Examples of the inorganic filler include metal hydroxides such asaluminium hydroxide, magnesium hydroxide, calcium hydroxide, chromiumhydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, orboron hydroxide; metal oxides such as alumina or zirconia; carbonatessuch as calcium carbonate or magnesium carbonate; sulfates such asbarium sulfate or calcium sulfate; and clay minerals such as calciumsilicate or talc. Among them, metal hydroxides metal oxides arepreferable, and from the viewpoint of imparting flame resistance or aneffect of electricity removal, metal hydroxides and metal oxides arepreferable, and magnesium hydroxide is particularly preferable. Aninorganic filler that is surface-modified with a silane coupling agentor the like can also be used. The inorganic fillers may be used singlyor in combination of two or more thereof.

The CPVC of the inorganic filler is preferably from 20% by volume to 70%by volume. When the CPVC of the inorganic filler is 70% by volume orless, pores are less likely to be occluded at the interface of a poroussubstrate and a heat resistant porous layer, and the separator has morefavorable ion permeability. When the CPVC of the inorganic filler is 70%by volume or less, the inorganic filler is less likely to fall off fromthe heat resistant porous layer. From these points of view, the CPVC ofthe inorganic filler is more preferably 65% by volume or less, furtherpreferably 60% by volume or less, and still further preferably 50% byvolume or less. On the other hand, when the CPVC of the inorganic filleris 20% by volume or more, the coating liquid has favorable coatingproperties in cases in which the heat resistant porous layer is formedby wet coating, and, therefore, occurrence of defects such as coatinglines is suppressed. From this point of view, the CPVC of the inorganicfiller is more preferably 30% by volume or more, and further preferably40% by volume or more.

The volume average particle diameter of the inorganic filler ispreferably from 0.01 μm to 10 μm. The lower limit thereof is morepreferably 0.1 μm, and the upper limit thereof is more preferably 5 μm.

The particle size distribution of the inorganic filler is preferably 0.1μm<d90−d10<3 μm. Here, dl 0 represents the particle diameter (μm) towhich the cumulative total of the particles in the particle sizedistribution from the smaller particle size side is 10% by mass, and d90represents the particle diameter (μm) to which the cumulative total ofthe particles in the particle size distribution from the particle sizeside is 10% by mass. The particle size distribution measurement isperformed, for example, by using a laser diffraction particle sizeanalyzer, by using water as a dispersion medium, and by using as neededa nonionic surfactant (for example, Triton X-100) as a dispersant.

The particle shape of the inorganic filler may be any shape, and may bespherical, elliptical, plate-shaped, rod-shaped, or irregular. From theviewpoint of preventing a short circuit of a battery, the inorganicfiller is preferably plate-shaped particles or primary particles thatare not aggregated.

The content of the inorganic filler in the heat resistant porous layeris preferably from 2.0 g/m² to 20.0 g/m². When the content of theinorganic filler is 2.0 g/m² or more, the thermal dimensional stabilityof the separator is more excellent. From this point of view, the contentof the inorganic filler is more preferably 2.5 g/m² or more, and furtherpreferably 3.0 g/m² or more. On the other hand, when the content of theinorganic filler is 20.0 g/m² or less, the heat resistant porous layeris less likely to be peeled off from the porous substrate. From thispoint of view, the content of the inorganic filler is more preferably15.0 g/m² or less, and further preferably 12.0 g/m² or less.

In the heat resistant porous layer, the inorganic filler preferablyaccounts for from 65% by mass to 99% by mass of the total amount ofresin particles and inorganic fillers. When the proportion of theinorganic filler is 65% by mass or more, the thermal dimensionalstability and ion permeability of the separator are excellent. From thispoint of view, the proportion of the inorganic filler is more preferably70% by mass or more, further preferably 73% by mass or more, stillfurther preferably 75% by mass or more, and still further preferably 80%by mass or more. On the other hand, when the proportion of the inorganicfiller is 99% by mass or less, the inorganic filler is less likely tofall off from the heat resistant porous layer, and the heat resistantporous layer is less likely to be peeled off from the porous substrate.From this point of view, the proportion of the inorganic filler is morepreferably 98.5% by mass or less, and still further preferably 98% bymass or less.

—Thickener—

The heat resistant porous layer may include a thickener. In the heatresistant porous layer that is formed of a coating liquid including athickener, unevenness of the resin particles and inorganic fillers issuppressed.

Example of the thickener include resins such as cellulose, polyvinylalcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethylene glycol,polypropylene glycol, polyacrylic acid, higher alcohols, and saltsthereof. Among them, cellulose and cellulose salts are preferable. Forexample, carboxymethylcellulose, hydroxyethylcellulose,hydroxypropylcellulose, methylcellulose, and a sodium salt or ammoniumsalt thereof are preferable.

From the viewpoint of the thermal dimensional stability, moisturecontent, and ion permeability of the separator, the proportion of thethickener with respect to the total amount of the resin particles,inorganic filler, and thickener is preferably 10% by mass or less, morepreferably 5% by mass or less, and further preferably 3% by mass orless. From the viewpoint of suppressing unevenness of the resinparticles and inorganic fillers in the heat resistant porous layer toimprove ion permeability, the proportion of the thickener with respectto the total amount of the resin particles, inorganic fillers, andthickener is preferably 0.1% by mass or more, more preferably 0.3% bymass or more, and further preferably 0.5% by mass or more.

—Other Ingredients—

The heat resistant porous layer may include ingredients other than theabove-mentioned compounds without inhibiting the effect of the presentinvention. Examples of the ingredients include a dispersant, a wettingagent, an antifoaming agent, and a pH adjusting agent which can be addedto a coating liquid for forming the heat resistant porous layer. It isnoted that the resin particles and the inorganic filler preferablyaccount for 90% by mass or more of the total amount of the heatresistant porous layer.

[Method of Forming Heat Resistant Porous Layer]

A method of forming the heat resistant porous layer on the poroussubstrate is not particularly limited. From the viewpoint of efficientlymanufacturing the separator, the following method is preferable. Namely,the preferable method is a method including: a coating process ofcoating a water-based dispersion including resin particles and aninorganic filler on one side or both sides of a porous substrate; and adrying process of drying the coated water-based dispersion.

Coating Process

The coating process is a process in which a water-based dispersionincluding resin particles and an inorganic filler is coated on one sideor both sides of a porous substrate.

The water-based dispersion is a coating liquid for forming a heatresistant porous layer, and is prepared by dispersing, suspending, oremulsifying resin particles and an inorganic filler in a solvent. As thesolvent of the water-based dispersion, at least water is used, andfurther, a solvent other than water may be added. The solvent other thanwater is not particularly limited as long as the solvent does notdissolve the resin particles and is capable of dispersing or suspendingthe resin particles in the solid state or emulsifying the resinparticles. Examples thereof include organic solvents such as methanol,ethanol, 2-propanol, acetone, tetrahydrofuran, methyl ethyl ketone,ethyl acetate, N-methylpyrrolidone, dimethylacetamide,dimethylformamide, or dimethylformamide. From the viewpoints of lowenvironmental load, safety, and economy, it is preferable to use awater-based emulsion obtained by emulsifying the resin particles and theinorganic filler in water or in a mixed liquid of water and alcohol.

The water-based dispersion may include a thickener for the purpose ofadjusting the viscosity to a value appropriate for coating on a poroussubstrate. The water-based dispersion may include a dispersant such as asurfactant for the purpose of enhancing the dispersibilities of theresin particles and inorganic filler. The water-based dispersion mayinclude a wetting agent for the purpose of improving the conformity witha porous substrate. The water-based dispersion may also include anantifoaming agent or a pH adjusting agent. Such additives may remain ina battery as long as the additives are electrochemically stable undercircumstances in which the battery is used and as long as the additivesdo not inhibit a reaction in the battery.

The content of the resin particles in the water-based dispersion ispreferably from 1% by mass to 25% by mass. The content of the inorganicfiller in the water-based dispersion is preferably from 2% by mass to50% by mass.

For coating the water-based dispersion onto a porous substrate, aconventional coating system using a Mayer bar, a die coater, a reverseroll coater, a gravure coater, a microgravure coater, spray coating, orthe like may be applied. In the case of forming a heat resistant porouslayer on both sides of the porous substrate, the water-based dispersionmay be coated on one side, then on the other side, and then subjected todrying, or may be coated simultaneously on both sides of the poroussubstrate, and then subjected to drying. From the viewpoint ofproductivity, the latter is preferable.

Drying Process

The drying process is a process in which the water-based dispersion thathas been coated on a porous substrate in the coating process is dried.By drying the water-based dispersion, the solvent is removed, and theresin particle functions as a binder, whereby the heat resistant porouslayer is fixed to the porous substrate.

The above mentioned forming method is a method in which a heat resistantporous layer is directly formed on a porous substrate by a wet coatingmethod. Alternatively, a heat resistant porous layer can be formed on aporous substrate by a method of bonding a sheet of a heat resistantporous layer which is separately manufactured on a porous substrateusing adhesives or the like or also by a method of heat sealing orcompression bonding.

[Characteristics of Heat Resistant Porous Layer]

From the viewpoint of heat resistance and handling properties, thethickness of the heat resistant porous layer is preferably 0.5 μm ormore per one side, and more preferably 1 μm or more per one side, andfrom the viewpoint of handling properties and battery capacity, thethickness of the heat resistant porous layer is preferably 15 μm or lessper one side, and more preferably 10 μm or less per one side. Both incases in which a heat resistant porous layer is provided on one side ofa porous substrate and in cases in which a heat resistant porous layeris provided on both sides of a porous substrate, the lower limit of thesum of the thicknesses is preferably 1 μm, more preferably 2 μm, andfurther preferably 3 μm, and the upper limit thereof is preferably 20μm, more preferably 15 μm, and further preferably 12 μm.

The porosity of the heat resistant porous layer is preferably from 40%to 70%. When the porosity of the heat resistant porous layer is 40% ormore, ion permeability of the separator is more excellent. From thispoint of view, the porosity is more preferably 45% or more, furtherpreferably 50% or more, and still further preferably 55% or more. On theother hand, when the porosity of the heat resistant porous layer is 70%or less, the thermal dimensional stability of the separator is moreexcellent. From this point of view, the porosity is more preferably 68%or less, and further preferably 65% or less.

In the heat resistant porous layer, the product of the porosity and theVf/CPVC is preferably from 40% to 60%. When the product is in the aboverange, both the ion permeability and the thermal dimensional stabilityof the separator can be easily attained. The lower limit thereof is morepreferably 43%, further preferably 45%, and the upper limit thereof ismore preferably 55%, and further preferably 50%.

[Characteristics of Separator According to First Embodiment]

From the viewpoint of the mechanical strength and the energy density ofa battery, the thickness of the separator according to the firstembodiment is preferably from 5 μm to 35 μm, more preferably from 5 μmto 30 μm, and further preferably from 10 μm to 25 μm.

From the viewpoint of mechanical strength, handling properties, and ionpermeability, the porosity of the separator according to the firstembodiment is preferably from 30% to 60%.

In view of good balance between the mechanical strength and the ionpermeability, the Gurley value (JIS P8117(2009)) of the separatoraccording to the first embodiment is preferably from 50 sec/100 cc to800 sec/100 cc, more preferably from 100 sec/100 cc to 500 sec/100 cc,and further preferably from 100 sec/100 cc to 400 sec/100 cc.

From the viewpoint of short circuit prevention, mechanical strength, andhandling properties, the piercing strength of the separator according tothe first embodiment is preferably from 250 g to 1000 g, more preferablyfrom 300 g to 1000 g, and further preferably from 300 g to 600 g.

From the viewpoint of the load characteristic of a battery, the filmresistance of the separator according to the first embodiment ispreferably from 0.5 ohm·cm² to 10 ohm·cm², and more preferably from 1ohm·cm² to 8 ohm·cm².

In a case in which the separator according to the first embodiment issubjected to a heat treatment at 150° C. for 30 minutes, the thermalshrinkage ratio of the separator according to the first embodiment inboth the MD direction and the TD direction is preferably 3% or less, andmore preferably 2% or less. When the thermal shrinkage ratio is in thisrange, the shape stability of a separator is high, thereby providing abattery in which a short circuit is less likely to occur even whenexposed to high temperatures.

In a case in which the separator is heated at a rate of temperatureincrease of 5° C./min. to the flow elongation deformation temperature ofthe thermoplastic resin, the thermal dimensional change ratio of theseparator according to the first embodiment in the MD direction ispreferably 3% or less, and more preferably 2% or less. When the thermaldimensional change ratio in the MD direction is in this range, a thermalstrain in the MD direction of the separator is small in a batterymanufactured by winding a separator and an electrode in the longitudinaldirection, and, therefore, a battery having a high heat resistance canbe provided.

In a case in which the separator according to the first embodiment isheated at a rate of temperature increase of 5° C./min. to the flowelongation deformation temperature of the thermoplastic resin, thethermal dimensional change ratio of the separator according to the firstembodiment in the TD direction is preferably 3% or less, and morepreferably 2% or less. When the thermal dimensional change ratio in theTD direction is in this range, the thermal strain of the separator inthe TD direction is small in a battery (cylindrical type battery, squaretype battery, laminate battery, or the like) manufactured by stacking aseparator and an electrode together, and, therefore, it is possible toprovide a battery having a high heat resistance. The width of theseparator does not need to be adjusted anticipating a thermaldeformation of the separator in the TD direction, thereby alsocontributing to the improvement of the battery capacity.

Specifically, the thermal dimensional change ratio is a temperaturedetermined by the following method. A separator is cut into a 3 mm (TDdirection)×16 mm (MD direction) piece and a 3 mm (MD direction)×16 mm(TD direction) piece. A sample is placed into a TMA measurement device,a TMA (thermomechanical analysis) is performed under the conditions suchthat the temperature-rising rate is 5° C./min. and the targettemperature is a flow elongation deformation temperature ofthermoplastic resin, while applying a load of 19.6 mN in thelongitudinal direction of the sample, and a TMA chart is prepared byplotting the temperature along the horizontal axis and the sample lengthalong the vertical axis for each of the MD direction and the TDdirection. From the TMA chart, the maximum change amount of theseparator is extracted, and the absolute value of the maximum changeamount is defined as a maximum deformation amount, and the thermaldimensional change ratio is calculated by the following formula.thermal dimensional change ratio (%) in MD direction=(maximumdeformation amount in MD direction)/(length in MD direction beforeheating)×100thermal dimensional change ratio (%) in TD direction=(maximumdeformation amount in TD direction)/((length in TD direction beforeheating)×100

The thermal shrinkage ratio and thermal dimensional change ratio of theseparator according to the first embodiment can be controlled by, forexample, the content of the inorganic filler in the heat resistantporous layer, the thickness of the heat resistant porous layer, theporosity of the heat resistant porous layer, the internal stress of thewhole separator, or the like.

<Separator for Non-Aqueous Secondary Battery According to SecondEmbodiment>

A separator according to a second embodiment includes a poroussubstrate, a heat resistant porous layer that is provided on one side orboth sides of the porous substrate, and an adhesive porous layer that isprovided on both sides of a stacked body of the porous substrate and theheat resistant porous layer. The heat resistant porous layer includes aresin and a filler, satisfies the following expression (2), and includesan adhesive resin.0.40≤Vf/CPVC≤0.99  expression (2)

In expression (2), Vf is the volume proportion (% by volume) of thefiller in the heat resistant porous layer, and CPVC is the criticalpigment volume concentration (% by volume) of the filler.

Since the separator according to the second embodiment includes a heatresistant porous layer, the separator has an excellent heat resistance.Since the separator according to the second embodiment includes adhesiveporous layers on both sides thereof, the separator has an excellentadhesion to an electrode, resulting in excellent cycle characteristics.A battery to which the separator of the second embodiment is applied isless likely to catch fire even when a foreign matter is trapped in thebattery.

In the separator according to the second embodiment, with regard to thefiller contained in the heat resistant porous layer, the ratio Vf/CPVCof the volume proportion (% by volume) of the filler to the CPVC(critical pigment volume concentration) (% by volume) of the filler isfrom 0.40 to 0.99. When the Vf/CPVC is 0.40 or larger, the thermalshrinkage ratio of the heat resistant porous layer is low, and safety ofthe battery can be secured. From this point of view, the Vf/CPVC ispreferably 0.45 or larger, and more preferably 0.50 or larger. On theother hand, when the Vf/CPVC is 0.99 or less, the filler is less likelyto fall off from a heat resistant porous layer, and the heat resistantporous layer is less likely to be peeled off from the porous substrate.Accordingly, the heat resistance can be maintained. From this point ofview, the Vf/CPVC is preferably 0.95 or less or less, and morepreferably 0.90 or less.

The CPVC (critical pigment volume concentration) of the filler is aphysical property obtained by measuring the linseed oil absorptionamount per unit mass in accordance with JIS K-5101-13-1 (2004) andcalculating using the following formula.CPVC (% by volume) of filler=linseed oil absorption amount per unit mass(ml/g)×specific gravity (g/cm³) of filler×100

The CPVC of the filler is a physical property determined by synthesizingfactors such as the material properties, particle size, particle sizedistribution, shape and the like of the filler, and can be controlled byadjusting each of these factors. For example, the CPVC can be adjustedby pulverizing the filler or adding thereto an filler having a differentparticle size.

The volume proportion Vf of the filler in the heat resistant porouslayer is calculated by the following formula.volume proportion Vf (% by volume) of filler=volume per unit area(cm³/m²) of filler÷volume per unit area (cm³/m²) of heat resistantporous layer×100

The volume per unit area (cm³/m²) of the filler is determined bydividing the weight per unit area (g/m²) of the filler by the specificgravity (g/cm³) of the filler. The volume per unit area (cm³/m²) of theheat resistant porous layer is determined by the product of thethickness of the heat resistant porous layer and the unit area. Theweight per unit area (g/m²) of the filler may also be determined by theweight per unit area (basis weight, g/m²) of the heat resistant porouslayer and the composition of the heat resistant porous layer, or may bedetermined by TGA (thermogravimetric analysis).

The volume proportion Vf of the filler in the heat resistant porouslayer can be controlled by the composition or porosity of the heatresistant porous layer.

Hereinafter, components of the separator according to the secondembodiment, and ingredients contained in each of the components aredescribed.

[Porous Substrate]

The porous substrate in the second embodiment has the same definition asthe porous substrate in the first embodiment. Specific embodiments andpreferable embodiments of the porous substrate in the second embodimentare the same as specific embodiments and preferable embodiments of theporous substrate in the first embodiment.

[Heat Resistant Porous Layer]

The separator according to the second embodiment includes a heatresistant porous layer on one side or both sides of the poroussubstrate. When the heat resistant porous layer is provided only on oneside of the porous substrate, the thickness of the whole separator canbe minimized, thereby contributing to improvement of the batterycapacity, and favorable ion permeability can be easily obtained due to asmall number of layers. On the other hand, when the heat resistantporous layer is provided on both sides of the porous substrate, the heatresistance of the separator is more excellent, and safety of a batterycan be improved. When the heat resistant porous layer is provided onboth sides of the porous substrate, a curl is less likely to begenerated on the separator.

In the second embodiment, the heat resistant porous layer is a layerthat includes a resin and a filler. The following embodiment A andembodiment B are preferable embodiments of the heat resistant porouslayer.

Embodiment A

A heat resistant porous layer of embodiment A is a layer including alarge number of micropores inside, and having a structure in whichmicropores communicate from one side to the other side, and is a layerthrough which gas or liquid can pass from one side to the other side. Asembodiment A, an embodiment in which a resin has a fibril shape to forma three-dimensional network structure, by which a filler is trapped; andan embodiment in which a resin is attached to at least part of thesurface of the filler to join the fillers with each other therebyforming a gap between the fillers when the content of the filler isrelatively large, are preferable.

Embodiment B

A heat resistant porous layer of embodiment B is an aggregate ofparticulate resin (resin particles) and a filler (an inorganic filler ispreferable). In other words, plural resin particles and plural fillerparticles are joined to form an aggregate in a layer form, and theaggregate is fixed on the surface of the porous substrate via at leastpart of the resin particles. The aggregate has a porous structure in alayer shape as a whole, and gas or liquid can pass from one side to theother side. Resin particles that are components of the aggregate arepreferably joined with each other and with fillers. The resin particleretaining its particle shape can be confirmed by observing the surfaceof the heat resistant porous layer with an SEM (scanning electronmicroscope). Embodiment B is superior to embodiment A in theproductivity of the separator.

—Resin—

As the resin, a resin that is stable with respect to an electrolyte,that is electrochemically stable, and that has a function of joining afiller is preferable.

When a material having a low heat resistance is used as a filler, aheat-resistant resin (a polymer having a melting point of 200° C. orhigher or a polymer not having a melting point and having adecomposition temperature of 200° C. or higher) is preferably used. Whena material whose heat resistance is excellent is used as a filler, aresin which is not heat resistant may be used, or a heat-resistant resinmay be used, and from the viewpoint of improving the heat resistance ofa separator, a heat-resistant resin preferably used.

Examples of the heat-resistant resin include a wholly aromaticpolyamide, polyamide-imide, polyimide, polysulfone, polyethersulfone,polyketone, polyether ketone, polyether imide, cellulose, and polyvinylalcohol. Among them, a wholly aromatic polyamide, polyamide-imide,polyimide, polyether imide, and polysulfone are preferable, from theviewpoint of excellent retention of an electrolyte.

Examples of resins other than heat-resistant resins include apolyvinylidene fluoride resin, polyolefin, polymethylpentene, andpolyester

Examples of a particulate resin (resin particle) include a particleincluding a resin such as a polyvinylidene fluoride resin, fluororubber, styrene-butadiene rubber, ethylene-acrylate copolymer,ethylene-acrylic acid copolymer, polyethylene, ethylene-vinyl acetatecopolymer, and a cross-linked acrylic resin. Among them, a particleincluding a polyvinylidene fluoride resin is preferable from theviewpoint of excellent oxidation resistance.

Examples of a polyvinylidene fluoride resin as a component of the resinparticle include homopolymers of vinylidene fluoride (polyvinylidenefluoride), and copolymers of vinylidene fluoride and another monomer(polyvinylidene fluoride copolymer), a mixture of polyvinylidenefluoride and an acrylic polymer, and a mixture of a polyvinylidenefluoride copolymer and an acrylic polymer.

Examples of the monomer that is copolymerizable with vinylidene fluorideinclude vinyl fluoride, chlorotrifluoroethylene, tetrafluoroethylene,hexafluoropropylene, trifluoroethylene, trichloroethylene,trifluoroperfluoropropylether, ethylene, (meth)acrylic acid, methyl(meth)acrylate, (meth)acrylic acid ester, vinyl acetate, vinyl chloride,and acrylonitrile. One of these monomers may be used singly or two ormore thereof may be used in combination.

The weight-average molecular weight of each of polyvinylidene fluorideand a polyvinylidene fluoride copolymer as a component of the resinparticle is preferably from 1,000 to 5,000,000, more preferably from10,000 to 2,000,000, and further preferably from 50,000 to 1,000,000.Each of polyvinylidene fluoride and a polyvinylidene fluoride copolymercan be synthesized by emulsion polymerization or suspensionpolymerization.

Examples of acrylic polymer as a component of the resin particle includea poly(meth)acrylic acid, a poly(meth)acrylate, a poly(meth)acrylic acidester, a cross-linked poly(meth)acrylic acid, a cross-linkedpoly(meth)acrylate, and a cross-linked poly(meth)acrylic acid ester, anda modified acrylic polymer may be used. One of these acrylic polymersmay be used singly or two or more thereof may be used in combination.

As a resin that is a component of the resin particle, it is preferableto use polyvinylidene fluoride, a copolymer of vinylidene fluoride andtetrafluoroethylene, a copolymer of vinylidene fluoride andhexafluoropropylene, a copolymer of vinylidene fluoride andtrifluoroethylene, a mixture of polyvinylidene fluoride and an acrylicpolymer, or a mixture of a polyvinylidene fluoride copolymer and anacrylic polymer. From the viewpoint of obtaining mechanical strengthwith which a battery can withstand an applied pressure or heat duringits manufacture, the polyvinylidene fluoride copolymer is preferably acopolymer that includes structural units derived from vinylidenefluoride in an amount of 50 mole % or more.

From the viewpoint of oxidation resistance, each of the mixture ofpolyvinylidene fluoride and an acrylic polymer and the mixture of apolyvinylidene fluoride copolymer and an acrylic polymer as componentsof the resin particle preferably includes polyvinylidene fluoride or apolyvinylidene fluoride copolymer in an amount of 20% by mass or more.

From the viewpoint of handling properties or manufacturability, thevolume average particle diameter of the resin particle is preferablyfrom 0.01 μm to 1 μm, more preferably from 0.02 μm to 1 μm, and furtherpreferably from 0.05 μm to 1 μm.

The content of the resin in the heat resistant porous layer ispreferably from 1% by mass to 50% by mass. When the content of the resinis 1% by mass or more, a filler is less likely to fall off from the heatresistant porous layer, and the heat resistant porous layer is lesslikely to be peeled off from the porous substrate, and the adhesiveporous layer is less likely to be peeled off from the heat resistantporous layer. From this point of view, the content of the resin is morepreferably 2% by mass or more, further preferably 3% by mass or more. Onthe other hand, when the content of the resin is 50% by mass or less,the thermal dimensional stability and ion permeability of the separatorare more excellent. From this point of view, the content of the resin ismore preferably 40% by mass or less, and further preferably 30% by massor less.

—Filler—

As the filler, a filler that is stable with respect to an electrolyteand that is electrochemically stable is preferable. The filler may beeither an organic filler or an inorganic filler. The filler may be usedsingly or in combination of two or more thereof.

Examples of the organic filler include crosslinked polymer particles ofa crosslinked poly(meth)acrylic acid, a crosslinked poly(meth)acrylicacid ester, a crosslinked polysilicone, a crosslinked polystyrene, acrosslinked polydivinylbenzene, a crosslinked product of astyrene-divinylbenzene copolymer, polyimide, a melamine resin, a phenolresin, a benzoguanamine-formaldehyde condensate, or the like; and heatresistant polymer particles of polysulfone, polyacrylonitrile, aramide,polyacetal, thermoplastic polyimide, or the like. Among them, acrosslinked poly(meth)acrylic acid, a crosslinked poly(meth)acrylic acidester, and a crosslinked polysilicone are preferable.

Examples of the inorganic filler include metal hydroxides such asaluminium hydroxide, magnesium hydroxide, calcium hydroxide, chromiumhydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, orboron hydroxide; metal oxides such as alumina or zirconia; carbonatessuch as calcium carbonate or magnesium carbonate; sulfates such asbarium sulfate or calcium sulfate; and clay minerals such as calciumsilicate or talc. Among them, metal hydroxides or metal oxides arepreferable, and from the viewpoint of imparting flame resistance or aneffect of electricity removal, metal hydroxides and metal oxides arepreferable, and magnesium hydroxide is particularly preferable. Aninorganic filler that is surface-modified with a silane coupling agentor the like can also be used.

The CPVC of the filler is preferably from 20% by volume to 80% byvolume. When the CPVC of the filler is 80% by volume or less, pores areless likely to be occluded at the interface of a heat resistant porouslayer and an adhesive porous layer, and the separator has more favorableion permeability. When the CPVC of the filler is 80% by volume or less,the thermal shrinkage ratio of the heat resistant porous layer can beminimized even when the amount of filler added is small, and the safetyof a battery can be secured. Further, when the CPVC of the filler is 80%by volume or less, the filler is less likely to fall off from the heatresistant porous layer. From these points of view, the CPVC of thefiller is more preferably 75% by volume or less, further preferably 70%by volume or less, and still further preferably 60% by volume or less.On the other hand, when the CPVC of the filler is 20% by volume or more,the coating liquid has favorable coating properties in cases in whichthe heat resistant porous layer is formed by wet coating, and,therefore, occurrence of defects such as coating lines is suppressed.From this point of view, the CPVC of the filler is more preferably 25%by volume or more, further preferably 40% by volume or more, and stillfurther preferably 43% by volume or more.

The volume average particle diameter of the filler is preferably from0.01 μm to 10 μm. The lower limit thereof is more preferably 0.1 μm, andthe upper limit thereof is more preferably 5 μm.

The particle size distribution of the filler is preferably 0.1μm<d90−d10<3 μm. Here, the d10 represents the particle diameter (μm) towhich the cumulative total of the particles in the particle sizedistribution from the smaller particle size side is 10% by mass, and thed90 represents the particle diameter (μm) to which the cumulative totalof the particles in the particle size distribution from the smallerparticle size side is 10% by mass. The particle size distributionmeasurement is performed, for example, by using a laser diffractionparticle size analyzer, by using water as a dispersion medium, and byusing as needed a nonionic surfactant (for example, Triton X-100) as adispersant.

The particle shape of the filler may be any shape, and may be spherical,elliptical, plate-shaped, rod-shaped, or irregular. From the viewpointof preventing a short circuit of a battery, the inorganic filler ispreferably a plate-shaped particle or a primary particle that is notaggregated.

The content of the filler in the heat resistant porous layer ispreferably from 2.0 g/m² to 20.0 g/m². When the content of the filler is2.0 g/m² or more, the heat resistance of the separator is moreexcellent. From this point of view, the content of the filler is morepreferably 2.5 g/m² or more, and further preferably 3.0 g/m² or more. Onthe other hand, when the content of the filler is 20.0 g/m² or less, theheat resistant porous layer is less likely to be peeled off from theporous substrate. From this point of view, the content of the filler ismore preferably 15.0 g/m² or less, and further preferably 12.0 g/m² orless.

In the heat resistant porous layer, the filler preferably accounts forfrom 50% by mass to 98% by mass of the total amount of the resin and thefiller. When the proportion of the filler is 50% by mass or more, thethermal dimensional stability and ion permeability of the separator areexcellent. From this point of view, the proportion of the filler is morepreferably 60% by mass or more, further preferably 65% by mass or more,still further preferably 70% by mass or more, still further preferably80% by mass or more, and still further preferably 85% by mass or more.On the other hand, when the proportion of the filler is 98% by mass orless, the filler is less likely to fall off from the heat resistantporous layer, and the heat resistant porous layer is less likely to bepeeled off from the porous substrate, and the adhesive porous layer isless likely to be peeled off from the heat resistant porous layer. Fromthis point of view, the proportion of the filler is more preferably97.5% by mass or less, further preferably 97% by mass or less, stillfurther preferably 95% by mass or less, and still further preferably 90%by mass or less.

—Thickener—

The heat resistant porous layer may include a thickener. In the heatresistant porous layer that is formed of a coating liquid including athickener, unevennness of the resin and the filler is suppressed.

Example of the thickener include resins such as cellulose, polyvinylalcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethylene glycol,polypropylene glycol, polyacrylic acid, higher alcohols, and saltsthereof. Among them, cellulose and a cellulose salts are preferable. Forexample, carboxymethylcellulose, hydroxyethylcellulose,hydroxypropylcellulose, methylcellulose, and sodium salts or ammoniumsalts thereof are preferable.

From the viewpoint of the thermal dimensional stability, moisturecontent, and ion permeability of the separator, the proportion of thethickener with respect to the total amount of the resin, the filler, andthe thickener is preferably 10% by mass or less, more preferably 5% bymass or less, and further preferably 3% by mass or less. From theviewpoint of inhibiting unevennness of the resin and the filler in theheat resistant porous layer to improve ion permeability, the proportionof the thickener with respect to the total amount of the resin, thefiller, and the thickener is preferably 0.1% by mass or more, morepreferably 0.3% by mass or more, and further preferably 0.5% by mass ormore.

—Other Ingredients—

The heat resistant porous layer may include ingredients other than theabove-mentioned compounds without inhibiting the effect of the presentinvention. Examples of the ingredients include a dispersant, a wettingagent, an antifoaming agent, and a pH adjusting agent which can be addedto a coating liquid for forming the heat resistant porous layer. It isnoted that the resin and the filler preferably account for 90% by massor more of the total amount of the heat resistant porous layer.

[Method of Forming Heat Resistant Porous Layer]

A method of forming the heat resistant porous layer on the poroussubstrate is not particularly limited. The heat resistant porous layercan be formed by, for example, the following method 1 or method 2.

—Method 1—

Method 1 is a method for forming a heat resistant porous layer ofembodiment A. Method 1 includes the following process A1 to process A5.

Process A1: Process of Manufacturing Slurry

A resin is dissolved in a solvent, and a filler is dispersed therein tomanufacture a slurry for forming a heat resistant porous layer. Thesolvent is not particularly limited as long as the solvent dissolves aresin. As the solvent, a polar solvent is preferable, and example of thepolar solvent include dimethyl sulfoxide, N,N-dimethylformamide,N,N-dimethylacetamide, and N-methyl-2-pyrrolidone. A solvent that is apoor solenon-poler solvent with respect to the resin can be added inaddition to the polar solvent. Application of a poor solvent induces amicro phase separation structure and facilitates making the heatresistant porous layer porous. As the poor solvent, alcohols arepreferred, and polyhydric alcohols such as glycol are particularlypreferable. The concentration of the resin in the slurry is preferablyfrom 4% by mass to 9% by mass. In cases in which an inorganic filler isused as the filler, when the dispersibility of the inorganic filler isnot preferable, the inorganic filler may be subjected to a surfacetreatment with a silane coupling agent or the like, thereby improvingthe dispersibility.

The slurry may include a thickener for the purpose of adjusting theviscosity to a value appropriate for coating on a porous substrate. Theslurry may include a dispersant such as a surfactant for the purpose ofenhancing the dispersibilities of the filler. The slurry may include awetting agent for the purpose of improving the conformity with a poroussubstrate. The slurry may also include an antifoaming agent or a pHadjusting agent. Such additives may remain in a battery as long as theadditives are electrochemically stable under circumstances in which thebattery is used and as long as the additives do not inhibit a reactionin the battery.

Process A2: Coating Process

The slurry is coated on one side or both sides of the porous substrate.When the heat resistant porous layer is formed on both sides of theporous substrate, simultaneous coating on both sides of the substrate ispreferable from the viewpoint of reduction of the process. Examples ofthe method of coating the slurry include a knife coater method, agravure coater method, a meyer-bar method, a die coater method, areverse roll coater method, a roll coater method, a screen printingmethod, an ink-jet method, and a spraying method. Among them, a reverseroll coater method is preferable from the viewpoint of forming a coatinglayer uniformly.

Process A3: Coagulation Process

A heat resistant porous layer is formed by coagulating the resin bytreating the slurry coated on the porous substrate with a coagulatingliquid. Examples of the treatment method using a coagulation liquidinclude: a method of spraying a coagulating liquid on a surface on whichthe slurry has been coated; and a method of immersing a porous substrateon which a slurry has been coated in a bath (coagulation bath)containing a coagulating liquid. The coagulating liquid may be a liquidwhich can coagulate the resin, and is preferably water, or a liquidobtained by adding water to the solvent which is used for the slurry.The mixing amount of water in the coagulation bath is preferably from40% by mass to 80% by mass from the viewpoint of the coagulationefficiency or from the viewpoint of making a heat resistant porous layerporous.

Process A4: Water Washing Process

The coagulating liquid in the coating layer is removed by washing thecoating layer after coagulation with water.

Process A5: Drying Process

The coating layer after washing is dried to remove water. A dryingmethod is not particularly limited. The drying temperature is preferablyfrom 50° C. to 80° C., and when a high drying temperature is applied, amethod of contacting a roll is preferably applied in order not to causea dimensional change due to thermal shrinkage.

—Method 2—

Method 2 is a method for forming a heat resistant porous layer ofembodiment B. Method 2 includes the following process B1 to process B3.

Process B1: Manufacturing Process of Slurry

A slurry for forming a heat resistant porous layer is prepared bydispersing, suspending, or emulsifying resin particles and a filler in asolvent. As the solvent, at least water is used, and further, a solventother than water may be added. The solvent other than water is notparticularly limited as long as the solvent does not dissolve the resinparticles and is capable of dispersing or suspending the resin particlesin the solid state or emulsifying the resin particles. Examples thereofinclude organic solvents such as methanol, ethanol, 2-propanol, acetone,tetrahydrofuran, methyl ethyl ketone, ethyl acetate,N-methylpyrrolidone, dimethylacetamide, dimethylformamide, ordimethylformamide. From the viewpoints of low load to the environment,safety, and economy, it is preferable to use a water-based emulsionobtained by emulsifying the resin particles and the inorganic filler inwater or in a mixed liquid of water and alcohol.

The slurry may include a thickener for the purpose of adjusting theviscosity to a value appropriate for coating on a porous substrate. Theslurry may include a dispersant such as a surfactant for the purpose ofenhancing the dispersibilities of the resin particles and filler. Theslurry may include a wetting agent for the purpose of improving theconformity with a porous substrate. The slurry may also include anantifoaming agent or a pH adjusting agent. Such additives may remain ina battery as long as the additives are electrochemically stable undercircumstances in which the battery is used and as long as the additivesdo not inhibit a reaction in the battery.

The content of the resin particles in the slurry is preferably from 1%by mass to 25% by mass. The content of the filler in the slurry ispreferably from 2% by mass to 50% by mass.

Process B2: Coating Process

In process B2, a process same as process A2 may be employed.

Process B3: Drying Process

By drying the slurry on the porous substrate, the solvent is removed,and the resin particle functions as a binder, whereby the coating layerincluding the resin particles and the filler is fixed to the poroussubstrate.

Each of method 1 and method 2 is a method in which a heat resistantporous layer is directly formed on a porous substrate by a wet coatingmethod. Alternatively, a heat resistant porous layer can be formed on aporous substrate by a method of bonding a sheet of a heat resistantporous layer which is separately manufactured on a porous substrateusing adhesives or the like or also by a method of heat sealing orcompression bonding.

[Characteristics of Heat Resistant Porous Layer]

From the viewpoint of heat resistance and handling properties, thethickness of the heat resistant porous layer is preferably 0.5 μm ormore per one side, and more preferably 1 μm or more per one side, andfrom the viewpoint of handling properties and battery capacity, thethickness of the heat resistant porous layer is preferably 5 μm or lessper one side. Both in cases in which a heat resistant porous layer isprovided on one side of a porous substrate and in cases in which heatresistant porous layer is provided on both sides of a porous substrate,the lower limit of the sum of the thicknesses is preferably 1 μm, morepreferably 2 μm, and further preferably 3 μm, and the upper limitthereof is preferably 10 μm, more preferably 8 μm, and furtherpreferably 5 μm.

The porosity of the heat resistant porous layer is preferably from 40%to 70%. When the porosity of the heat resistant porous layer is 40% ormore, ion permeability of the separator is more excellent. From thispoint of view, the porosity is more preferably 45% or more, furtherpreferably 50% or more, and still further preferably 55% or more. On theother hand, when the porosity of the heat resistant porous layer is 70%or less, the thermal dimensional stability of the separator is moreexcellent. From this point of view, the porosity is more preferably 68%or less, and further preferably 65% or less.

[Adhesive Porous Layer]

In the second embodiment, an adhesive porous layers is provided on bothsides of the separator as the outermost layer, and the adhesive porouslayer is a layer which includes an adhesive resin and which can bond toan electrode. Since the separator according to the second embodimentincludes the adhesive porous layers on both sides of the separator, theseparator has an excellent adhesion to both electrodes of a battery.Since the separator according to the second embodiment includes theadhesive porous layers on both sides of the separator, a battery hasexcellent cycle characteristics (capacity retention rate) compared withcases in which a separator includes the layer on one side.

Preferable embodiments of the adhesive porous layer are the followingembodiment A′ and embodiment B′.

Embodiment A′

An adhesive porous layer of embodiment A′ is a layer including a largenumber of micropores inside, and having a structure in which microporescommunicate from one side to the other side, and is a layer throughwhich gas or liquid can pass from one side to the other side. Asembodiment A′, an embodiment in which a resin has a fibril shape to forma three-dimensional network structure is preferable, and when a filleris contained, an embodiment in which a filler is trapped by the networkstructure is preferable.

Embodiment B′

A adhesive porous layer of embodiment B′ is an aggregate of particulateresin (resin particles). In other words, plural resin particles arejoined to form a layered aggregate, and the aggregate is fixed on thesurface of the porous substrate or heat resistant porous layer via atleast part of the resin particles. The aggregate has a porous structurein a layer shape as a whole, and gas or liquid can pass from one side tothe other side. When a filler is contained, an embodiment in which aresin particle is joined with a filler to form an aggregate ispreferable.

—Adhesive Resin—

An adhesive resin contained in the adhesive porous layer is notparticularly limited as long as the adhesive resin is capable of bondingto an electrode. For example, polyvinylidene fluoride resins such aspolyvinylidene fluoride and a polyvinylidene fluoride copolymer; fluororubber; a styrene-butadiene copolymer; a homopolymer or copolymer ofvinyl nitriles such as acrylonitrile and methacrylonitrile; cellulosesuch as carboxymethylcellulose and hydroxyalkyl cellulose; polyvinylcompounds such as polyvinyl alcohol, polyvinyl butyral, and polyvinylpyrrolidone; and polyethers such as polyethylene oxide and polypropyleneoxide are preferable. Among them, polyvinylidene fluoride resins arepreferable. The adhesive porous layer may contain one adhesive resin ormay contain two or more adhesive resins.

Examples of the polyvinylidene fluoride resins include homopolymer ofvinylidene fluoride (polyvinylidene fluoride), copolymer of vinylidenefluoride and another monomer (polyvinylidene fluoride copolymer), and amixture thereof. Examples of the vinylidene fluoride and copolymerizablemonomer include hexafluoropropylene, tetrafluoroethylene,trifluoroethylene, trichloroethylene, and vinyl fluoride, and one or twoor more thereof can be used. Polyvinylidene fluoride resins can besynthesized by emulsion polymerization or suspension polymerization.

The polyvinylidene fluoride resin preferably contains vinylidenefluoride as a structural unit in an amount of 95 mole % or more (morepreferably 98 mole % or more). When vinylidene fluoride is contained inan amount of 95 mole % or more, mechanical strength and heat resistancewith which a battery can withstand an applied pressure or heat duringits manufacture can be easily secured.

As the polyvinylidene fluoride resin, from the viewpoint of adhesion toan electrode, a copolymer of vinylidene fluoride and hexafluoropropyleneis preferable, and a copolymer including from 0.1 mole % to 5 mole %(preferably 0.5 mole % to 2 mole %) of structural units derived fromhexafluoropropylene is more preferable.

The weight-average molecular weight of the adhesive resin (inparticular, polyvinylidene fluoride resin) is preferably from 300,000 to3,000,000. When the weight-average molecular weight is 300,000 or more,mechanical characteristics with which the adhesive porous layer canwithstand the adhesion treatment with an electrode can be secured,thereby obtaining sufficient adhesion. On the other hand, when theweight-average molecular weight is 3,000,000 or less, the viscosity of acoating liquid which is used during coat molding does not become toohigh, favorable moldability and crystal formation are obtained, and anadhesive porous layer that is favorably porous is obtained. Theweight-average molecular weight is more preferably from 300,000 to2,000,000, further preferably from 500,000 to 1,500,000, andparticularly preferably from 600,000 to 1,000,000.

Examples of a particulate resin (resin particle) include a particleincluding a resin such as a polyvinylidene fluoride resin, fluororubber, styrene-butadiene rubber, ethylene-acrylate copolymer,ethylene-acrylic acid copolymer, polyethylene, ethylene-vinyl acetatecopolymer, and a cross-linked acrylic resin. Among them, a particleincluding a polyvinylidene fluoride resin is preferable from theviewpoint of excellent oxidation resistance.

Examples of a polyvinylidene fluoride resin as a component of the resinparticle include homopolymers of vinylidene fluoride (polyvinylidenefluoride), copolymers of vinylidene fluoride and another monomer(polyvinylidene fluoride copolymer), a mixture of polyvinylidenefluoride and an acrylic polymer, and a mixture of a polyvinylidenefluoride copolymer and an acrylic polymer.

Examples of the monomer that is copolymerizable with vinylidene fluorideinclude vinyl fluoride, chlorotrifluoroethylene, tetrafluoroethylene,hexafluoropropylene, trifluoroethylene, trichloroethylene,trifluoroperfluoropropylether, ethylene, (meth)acrylic acid, methyl(meth)acrylate, (meth)acrylic acid ester, vinyl acetate, vinyl chloride,and acrylonitrile. One of these monomer may be used singly or two ormore thereof may be used in combination.

The weight-average molecular weight of each of polyvinylidene fluorideand a polyvinylidene fluoride copolymer as a component of the resinparticle are preferably from 1,000 to 5,000,000, more preferably from10,000 to 2,000,000, and further preferably from 50,000 to 1,000,000.Each of Polyvinylidene fluoride and a polyvinylidene fluoride copolymercan be synthesized by emulsion polymerization or suspensionpolymerization.

Examples of acrylic polymer as a component of the resin particle includea poly(meth)acrylic acid, a poly(meth)acrylic acid salt, apoly(meth)acrylic acid ester, a cross-linked poly(meth)acrylic acid, across-linked poly(meth)acrylic acid salt, and a cross-linkedpoly(meth)acrylic acid ester, and a modified acrylic polymer may beused. One of these acrylic polymers may be used singly or two or morethereof may be used in combination.

As a resin that is a component of the resin particle, it is preferableto use polyvinylidene fluoride, a copolymer of vinylidene fluoride andtetrafluoroethylene, a copolymer of vinylidene fluoride andhexafluoropropylene, a copolymer of vinylidene fluoride andtrifluoroethylene, a mixture of polyvinylidene fluoride and an acrylicpolymer, or a mixture of a polyvinylidene fluoride copolymer and anacrylic polymer. From the viewpoint of obtaining mechanical strengthwith which a battery can withstand an applied pressure or heat duringits manufacture, the polyvinylidene fluoride copolymer is preferably acopolymer that includes structural units derived from vinylidenefluoride in an amount of 50 mole % or more.

From the viewpoint of oxidation resistance, each of the mixture ofpolyvinylidene fluoride and an acrylic polymer and the mixture of apolyvinylidene fluoride copolymer and an acrylic polymer, as a componentof the resin particle, preferably include polyvinylidene fluoride or apolyvinylidene fluoride copolymer in an amount of 20% by mass or more.

From the viewpoint of handling properties or manufacturability, thevolume average particle diameter of the resin particles is preferablyfrom 0.01 μm to 1 μm, more preferably from 0.02 μm to 1 μm, and furtherpreferably from 0.05 μm to 1 μm.

—Filler—

The adhesive porous layer may include a filler. As the filler, a fillerthat is stable with respect to an electrolyte, that is electrochemicallystable, and that has a function of joining an inorganic filler ispreferable. The filler may be either an organic filler or an inorganicfiller, and specific examples thereof include the fillers described asexamples of the filler contained in a heat resistant porous layerillustrated above. The filler may be used singly or in combination oftwo or more thereof.

When the adhesive porous layer includes a filler, the proportion of thefiller with respect to the total amount of the resin and the filler ispreferably from 1% by mass to 30% by mass.

[Method of Forming Adhesive Porous Layer]

A method of forming an adhesive porous layer is not particularlylimited. An adhesive porous layer can be formed by a method similar tomethod 1 or method 2 of forming a heat resistant porous layer.

[Characteristics of Adhesive Porous Layer]

From the viewpoint of adhesion to an electrode and ion permeability, thethickness of the adhesive porous layer per one side is preferably from0.5 μm to 10 μm, and more preferably from 1 μm to 5 μm.

From the viewpoint of adhesion to an electrode and ion permeability, thecoating amount of the adhesive porous layer is preferably from 0.5 g/m²to 3.5 g/m² in total on both sides.

From the viewpoint of ion permeability, the adhesive porous layerpreferably has a structure which is sufficiently porous, and theporosity is preferably from 30% to 70%. When the porosity is 70% orless, mechanical strength with which the adhesive porous layer canwithstand an applied pressure or heat during battery manufacture can besecured. When the porosity is 70% or less, the surface aperture ratio isnot too high, and favorable adhesion to an electrode is attained. Fromthese points of view, the porosity is more preferably 60% or less. Onthe other hand, when the porosity is 30% is 30% or more, favorable ionpermeability is attained. From this point of view, the porosity is morepreferably 35% or more, further preferably 40% or more, and furtherpreferably 45% or more.

The peel strength between the heat resistant porous layer and theadhesive porous layer is preferably 0.05 N/cm or more, more preferably0.06 N/cm or more, and further preferably 0.07 N/cm or more.

[Characteristics of Separator According to Second Embodiment]

From the viewpoint of mechanical strength and energy density of abattery, the thickness of the separator according to the secondembodiment is preferably from 5 μm to 35 μm, more preferably from 5 μmto 30 μm, and further preferably from 10 μm to 25 μm.

From the viewpoint of mechanical strength, handling properties, and ionpermeability, the porosity of the separator according to the secondembodiment is preferably from 30% to 60%.

From the viewpoint of obtaining favorable ion permeability, the averageof the porosity of the heat resistant porous layer and the porosity ofthe adhesive porous layer of the separator according to the secondembodiment is preferably from 30% to 70%. The lower limit thereof ismore preferably 35%, further preferably 40%, and further preferably 45%,and the upper limit is more preferably 65%, and further preferably 60%.

The average of the porosity of the heat resistant porous layer and theporosity of the adhesive porous layer is calculated by the followingformula. In the formula below, each of the thickness of the heatresistant porous layer and the thickness of the adhesive porous layer isthe total value of both sides thereof.average porosity (%)={porosity (%) of heat resistant porouslayer×thickness (μm) of heat resistant porous layer+porosity (%) ofadhesive porous layer×thickness (μm) of adhesive porouslayer}÷{thickness (μm) of heat resistant porous layer+thickness (μm) ofadhesive porous layer}

In view of good balance between the mechanical strength and the ionpermeability, the Gurley value (JIS P8117(2009)) of the separatoraccording to the second embodiment is preferably from 50 sec/100 cc to800 sec/100 cc, more preferably from 100 sec/100 cc to 500 sec/100 cc,and further preferably from 100 sec/100 cc to 400 sec/100 cc.

From the viewpoint of ion permeability, the tortuosity of the separatoraccording to the second embodiment is preferably 1.5 to 2.5.

From the viewpoint of short circuit prevention, mechanical strength, andhandling properties, the piercing strength of the separator according tothe second embodiment is preferably from 250 g to 1000 g, morepreferably from 300 g to 1000 g, and further preferably from 300 g to600 g.

From the viewpoint of short circuit prevention, mechanical strength, andhandling properties, the tensile strength of the separator according tothe second embodiment is preferably 10 N or more.

From the viewpoint of the load characteristic of a battery, the filmresistance of the separator according to the second embodiment ispreferably from 0.5 ohm·cm² to 10 ohm·cm², and more preferably from 1ohm·cm² to 8 ohm·cm².

The shutdown temperature of the separator according to the secondembodiment is preferably from 130° C. to 155° C. when a porous substrateformed of a polyolefin is used.

In a case in which the separator according to the second embodiment issubjected to a heat treatment at 150° C. for 30 minutes, the thermalshrinkage ratio of the separator according to the second embodiment inthe MD direction is preferably 20% or less, and more preferably 10% orless, and the thermal shrinkage ratio of the separator according to thesecond embodiment in the TD direction is preferably 10% or less, andmore preferably 5% or less. When the thermal shrinkage ratio is in thisrange, the shape stability of a separator is high, and, therefore, it ispossible to provide a battery in which a short circuit is less likely tooccur even when exposed to high temperatures.

In a case in which the separator according to the second embodiment issubjected to a heat treatment at 130° C. for 30 minutes, the thermalshrinkage ratio of the separator according to the second embodiment inthe MD direction is preferably 10% or less, and more preferably 8% orless, and the thermal shrinkage ratio of the separator according to thesecond embodiment in the TD direction is preferable 5% or less, and morepreferably 3% or less. When the thermal shrinkage ratio is in thisrange, the shape stability of a separator is high, and, therefore, it ispossible to provide a battery in which a short circuit is less likely tooccur even when exposed to high temperatures.

In a case in which the separator according to the second embodiment isheated at a rate of temperature increase of 5° C./min. to the flowelongation deformation temperature of the thermoplastic resin, thethermal dimensional change ratio of the separator according to thesecond embodiment in the MD direction is preferably 3% or less, and morepreferably 2% or less. When the thermal dimensional change ratio in theMD direction is in this range, a thermal strain in the MD direction ofthe separator is small in a battery manufactured by winding a separatorand an electrode in the longitudinal direction, and, therefore, it ispossible to provide a battery having a high heat resistance.

In a case in which the separator according to the second embodiment isheated at a rate of temperature increase of 5° C./min. to the flowelongation deformation temperature of the thermoplastic resin, thethermal dimensional change ratio of the separator according to thesecond embodiment in the TD direction is preferably 3% or less, and morepreferably 2% or less. When the thermal dimensional change ratio in theTD direction is in this range, the thermal strain of the separator inthe TD direction is small in a battery (cylindrical type battery, squaretype battery, laminate battery, or the like) manufactured by stacking aseparator and an electrode together, and, therefore, it is possible toprovide a battery having a high heat resistance. The width of theseparator does not need to be adjusted anticipating a thermaldeformation of the separator in the TD direction, thereby alsocontributing to the improvement of the battery capacity.

Specifically, the above-described thermal dimensional change ratio is atemperature determined by the following method. A separator is cut intoa 3 mm (TD direction)×16 mm (MD direction) piece and a 3 mm (MDdirection)×16 mm (TD direction) piece. A sample is placed into a TMAmeasurement device, a TMA (thermomechanical analysis) is performed underthe conditions such that the temperature-rising rate is 5° C./min. andthe target temperature is the flow elongation deformation temperature ofthermoplastic resin, while applying a load of 19.6 mN in thelongitudinal direction of the sample, and a TMA chart is prepared byplotting the temperature along the horizontal axis and the sample lengthalong the vertical axis for each of the MD direction and the TDdirection. From the TMA chart, the maximum change amount of theseparator is extracted, and the absolute value of the maximum changeamount is defined as a maximum deformation amount, and the thermaldimensional change ratio is calculated by the following formula.thermal dimensional change ratio (%) in MD direction=(maximumdeformation amount in MD direction)/(length in MD direction beforeheating)×100thermal dimensional change ratio (%) in TD direction=(maximumdeformation amount in TD direction)/((length in TD direction beforeheating)×100

The thermal shrinkage ratio and thermal dimensional change ratio of theseparator according to the second embodiment can be controlled by, forexample, the content of the filler in the heat resistant porous layer,the thickness of the heat resistant porous layer, the thickness of theheat resistant porous layer, the average of the porosity of the heatresistant porous layer and the porocity of the adhesive porous layer,the internal stress of the whole separator, or the like.

<Non-Aqueous Secondary Battery>

The non-aqueous secondary battery of the present invention is anon-aqueous secondary battery in which electromotive force is obtainedby lithium doping/dedoping, and which includes a positive electrode, anegative electrode, and a separator for a non-aqueous secondary batteryof the present invention. A non-aqueous secondary battery has astructure in which a battery element in which a construct in which anegative electrode and a positive electrode are faced to each other viaa separator is impregnated with an electrolyte is enclosed in an outercasing member. The term “dope” means occlusion, support, adsorption, orinsertion, and means a phenomenon in which a lithium ion enters into anactive material of an electrode.

The non-aqueous secondary battery of the present invention is excellentin battery characteristics and safety when at least one of the separatorof the first embodiment and the separator of the second embodiment isapplied.

In the non-aqueous secondary battery of the present invention, when theseparator of the first embodiment is applied, it is preferable from theviewpoint of the durability of a battery that a heat resistant porouslayer of the separator includes olyvinylidene fluoride resin particlesand the separator is disposed such that the heat resistant porous layeris in contact with a positive electrode. In general, oxidizingatmosphere of a positive electrode has an influence on the durability ofa non-aqueous secondary battery; however, since a polyvinylidenefluoride resin has a high oxygen index and a high oxidation resistance,the surface of a separator is less likely to be oxidized or carbonizedwhen a heat resistant porous layer including the resin is disposed so asto be in contact with a positive electrode, and then the battery hasfavorable durability.

In the non-aqueous secondary battery of the present invention, when theseparator of the second embodiment is applied, it is preferable from theviewpoint of the durability of a battery that an adhesive porous layerof the separator includes a polyvinylidene fluoride resin. In general,oxidizing atmosphere of a positive electrode has an influence on thedurability of a non-aqueous secondary battery; however, since apolyvinylidene fluoride resin has a high oxygen index and a highoxidation resistance, the surface of a separator is less likely to beoxidized or carbonized when the adhesive porous layer include the resin,and then the battery has favorable durability.

The non-aqueous secondary battery of the present invention is suitablefor non-aqueous electrolyte secondary batteries, in particular forlithium ion secondary batteries.

[Positive Electrode]

The positive electrode may have a structure in which an active materiallayer including a positive electrode active material and a binder resinis formed on a current collector. The active material layer may furtherinclude an electrically conductive additive.

Examples of the positive electrode active material includelithium-containing transition metal oxides, and specific examplesthereof include LiCoO₂, LiNiO₂, LiMn_(1/2)Ni_(1/2)O₂,LiCo_(1/3)Mn_(1/3)Ni_(1/3)O₂, LiMn₂O₄, LiFePO₄, LiCo_(1/2)Ni_(1/2)O₂,and LiAl_(1/4)Ni_(3/4)O₂.

A positive electrode active material which can be operated at a highvoltage of 4.2 V or more, such as LiMn_(1/2)Ni_(1/2)O₂ orLiCo_(1/3)Mn_(1/3)Ni_(1/3)O₂, is desirably in combination with aseparator including a polyvinylidene fluoride resin in a layer which isin contact with a positive electrode.

Examples of the binder resin include a polyvinylidene fluoride resin.

Examples of the electrically conductive additive include a carbonmaterial such as acetylene black, Ketjen black, or graphite powder.

Examples of the current collector include aluminum foil, titanium foil,and stainless foil having a thickness of from 5 μm to 20 μm.

[Negative Electrode]

The negative electrode may have a structure in which an active materiallayer containing a negative electrode active material and a binder resinis formed on a current collector. The active material layer may furthercontain an electrically conductive additive.

Examples of the negative electrode active material include materialscapable of electrochemically occluding lithium. Specific examplesinclude carbon materials, and alloys of lithium and silicon, tin,aluminium, or the like.

Examples of the binder resin include polyvinylidene fluoride resins andstyrene-butadiene rubbers.

Examples of the electrically conductive additive include carbonmaterials such as acetylene black, Ketjen black, or graphite powder.

Examples of the current collector include a copper foil, a nickel foil,and a stainless steel foil, each having a thickness of from 5 μm to 20μm.

Instead of using the negative electrode described above, a metal lithiumfoil may be used as the negative electrode.

[Electrolyte]

The electrolyte is a solution obtained by dissolving a lithium salt in anon-aqueous solvent.

Examples of the lithium salt include LiPF₆, LiBF₄, and LiClO₄.

Examples of the non-aqueous solvent include cyclic carbonates such asethylene carbonate, propylene carbonate, fluoroethylene carbonate, ordifluoroethylene carbonate; chain carbonates such as dimethyl carbonate,diethyl carbonate, ethyl methyl carbonate, or a fluorine substitutionproduct thereof; cyclic esters such as γ-butyrolactone orγ-valerolactone; and the like. These non-aqueous solvents may be usedsingly or in mixture.

As the electrolyte, a solution is preferred, which is obtained by mixinga cyclic carbonate and a chain carbonate at a mass ratio (cycliccarbonate/chain carbonate) of from 20/80 to 40/60, and dissolving alithium salt to give a concentration of from 0.5 M to 1.5 M.

[Manufacture Method of Non-Aqueous Secondary Battery]

The non-aqueous secondary battery of the invention can be manufactured,for example, by a method in which a stacked body in which the separatorof the invention is disposed between a positive electrode and a negativeelectrode is impregnated with an electrolyte, and housed in an outercasing member, and the stacked body is pressed from above the outercasing member.

A system of disposing a separator between a positive electrode and anegative electrode may be a system of stacking a positive electrode, aseparator, and a negative electrode on one another, each by at least onelayer, in this order (a so-called stack system) or may be a system inwhich a positive electrode, a separator, a negative electrode, and aseparator are stacked together in the order mentioned and wound in thelength direction.

Examples of the outer casing member include a metal can and an aluminumlaminated film pack.

Since adhesion to electrodes is suitable when a separator having anoutermost surface layer containing a polyvinylidene fluoride resin, aspace is hardly formed between the electrode and the separator, even ifimpact from the outside is applied or expansion/shrinkage of theelectrode occurs during charging and discharging. Thus, the separator ofthe invention is suitable for use in an aluminum laminated film pack asthe outer casing material.

Examples of the shape of a battery include a square type, a cylindricaltype, and a coin type. The separator of the invention is suitable forany shape.

EXAMPLES

Hereinafter, the present invention is described in further detail withreference to Examples. The Material, amount of use, proportion,procedure, or the like described below can be appropriately modifiedwithout deviating from the spirit of the present invention. Therefore,the scope of the present invention should not be construed to be limitedby the following specific examples.

<Measurement Method>

The following measurement methods were applied in the Examples of thepresent invention and the Comparative Examples.

[Weight-Average Molecular Weight of Resin]

The weight-average molecular weight of the resin was determined by gelpermeation chromatography (GPC).

Device: Gel permeation chromatograph ALLIANCE GPC2000 type (manufacturedby Waters)

Column: TSKgel GMH6-HT×2, TSKgel GMH6-HTL×2 (manufactured by TosohCorporation)

Column Temperature: 140° C.

Mobile Phase: o-dichlorobenzene

Column Temperature: 140° C.

Reference Material for Molecular Weight Calibration: MonodispersePolystyrene (manufactured by Tosoh Corporation)

[Composition of Polyvinylidene Fluoride Resin]

20 mg of a polyvinylidene fluoride resin was dissolved in 0.6 ml ofheavy dimethyl sulfoxide at 100° C., ¹⁹F-NMR spectrum was measured at100° C., and the composition of the polyvinylidene fluoride resin wasdetermined from the NMR spectrum.

[Average Particle Diameter of Resin Particle]

Resin particles were dispersed in water to measure the particle diameterof the resin particle by using a laser diffraction particle sizeanalyzer (MASTERSIZER 2000 manufactured by SYSMEX CORPORATION), and themedian particle diameter (D50) in the volume particle size distributionwas designated as the average particle diameter.

[CPVC of Filler]

The linseed oil absorption amount per unit mass was measured inaccordance with JIS K-5101-13-1(2004), and the CPVC of the filler wascalculated by the following formula.CPVC (% by volume) of filler=linseed oil absorption amount per unit mass(ml/g)×specific gravity (g/cm³) of filler×100

[Volume Proportion Vf of Filler]

The volume proportion Vf of the filler in the heat resistant porouslayer was calculated by the following formula.volume proportion Vf (% by volume) of filler=volume per unit area(cm³/m²) of filler/volume per unit area (cm³/m²) of heat resistantporous layer×100

The volume per unit area (cm³/m²) of the filler was obtained by dividingthe weight per unit area (g/m²) of the filler by the specific gravity(g/cm³) of the filler. The weight per unit area (g/m²) of the filler wasdetermined by the weight per unit area (basis weight, g/m²) of the heatresistant porous layer and the composition ratio of the filler of thecoating liquid for forming a heat resistant porous layer. The volume perunit area (cm³/m²) of the heat resistant porous layer was determined bythe product of the thickness of the heat resistant porous layer and unitarea.

[Film Thickness]

The film thickness (μm) of the separator or the like was determined bymeasuring arbitrary 20 points in a 10 cm×30 cm area with a contact typethickness gauge (LITEMATIC manufactured by Mitutoyo Corporation), andaveraging the measured values. The measuring probe used had acylindrical shape having a diameter 5 mm, and adjustment was performedsuch that a load of 7 g was applied during measurement.

The thickness of the heat resistant porous layer was determined bysubtracting the thickness of the porous substrate from the thickness ofa stacked body of the porous substrate and a heat resistant porouslayer. The thickness of the adhesive porous layer was determined bysubtracting the thickness of a stacked body of the porous substrate, theheat resistant porous layer and the adhesive porous layer from thethickness of a stacked body of the porous substrate and the heatresistant porous layer.

[Basis Weight]

The basis weight (mass per 1 m²) was determined by cutting a sample intoa 10 cm×30 cm piece, measuring the mass of the piece, and dividing themass by the area.

[Content of Filler in Heat Resistant Porous Layer]

By subtracting the basis weight of the porous substrate from the basisweight of a stacked body of the porous substrate and the heat resistantporous layer, the mass per unit area (g/m²) of the heat resistant porouslayer was determined. The content (g/m²) of the filler in the heatresistant porous layer was then calculated from the composition ratio ofthe filler of the coating liquid for forming a heat resistant porouslayer. The thus calculated content of the filler is the total amount onboth sides of the porous substrate.

[Porosity]

The porosity of each layer was determined by the following calculationmethod.

Setting the constituent materials to a, b, c, . . . , n, the weights ofthe constituent materials to Wa, Wb, Wc, . . . , Wn(g/cm²), the truedensities of the constituent materials da, db, dc, . . . , dn (g/cm³),and the film thickness of a layer of interest to t(cm), the porosity ε(%) is determined by the following formula.ε={1−(Wa/da+Wb/db+We/dc+ . . . +Wn/dn)/t}×100

The average of the porosity of the heat resistant porous layer and theporosity of the adhesive porous layer (the average porocity of thecoating layer) was calculated by the following formula. In the followingformula, each of the thicknesses of the heat resistant porous layer andthe thickness of the adhesive porous layer is the total value of bothsides thereof.average porosity (%)={porosity (%) of heat resistant porouslayer×thickness (μm) of heat resistant porous layer+porosity (%) ofadhesive porous layer×thickness (μm) of adhesive porouslayer}÷{thickness (μm) of heat resistant porous layer+thickness (μm) ofadhesive porous layer}

[Gurley Value]

The Gurley value (sec/100 cc) was measured by using a Gurley typedensometer (G-B2C, manufactured by Toyo Seiki Sensaku-Sho, Ltd.) inaccordance with JIS P8117 (2009).

[Flow Elongation Deformation Temperature of Thermoplastic Resin]

A porous substrate was cut into a 3 mm (TD direction)×16 mm (MDdirection) piece and a 3 mm (MD direction)×16 mm (TD direction) piece. Asample was placed into a TMA measurement device (Q400 V22.4 Build 30manufactured by TA Instruments Japan Inc.), a TMA (thermomechanicalanalysis) was performed at a temperature-rising rate of 5° C./min. whileapplying a load of 19.6 mN in the longitudinal direction of the sample,and a TMA chart was prepared by plotting the temperature along thehorizontal axis and the sample length along the vertical axis for eachof the MD direction and the TD direction. For each of the MD directionand the TD direction, the temperature at which the elongation percentageof the sample was 15% was determined from the TMA chart, and the averageof the temperatures for the MD direction and the TD direction wascalculated, thereby obtaining the flow elongation deformationtemperature of a thermoplastic resin that is a component of the poroussubstrate.

[Thermal Dimensional Change Ratio]

A separator was cut into a 3 mm (TD direction)×16 mm (MD direction)piece and a 3 mm (MD direction)×16 mm (TD direction) piece. A sample wasplaced into a TMA measurement device (Q400 V22.4 Build 30 manufacturedby TA Instruments Japan Inc.) to perform a TMA under conditions suchthat the temperature-rising rate was 5° C./min. and the targettemperature was the flow elongation deformation temperature ofthermoplastic resin, while applying a load of 19.6 mN in thelongitudinal direction of the sample, a TMA chart was prepared byplotting the temperature along the horizontal axis and the sample lengthalong the vertical axis for each of the MD direction and the TDdirection. From the TMA chart, the maximum change amount of theseparator was extracted, the absolute value of the maximum change amountwas defined as a maximum deformation amount, and the thermal dimensionalchange ratio was calculated by the following formulae.thermal dimensional change ratio (%) in MD direction=(maximumdeformation amount in MD direction)/(length in MD direction beforeheating)×100thermal dimensional change ratio (%) in TD direction=(maximumdeformation amount in TD direction)/((length in TD direction beforeheating)×100

[Thermal Shrinkage Ratio]

A separator was cut into a 18 cm (MD direction)×6 cm (TD direction) testpiece. On a line which divides the test piece into two in the TDdirection, two marks were placed on two points (point A and point B) at2 cm and 17 cm from one end, respectively. On a line which divides thetest piece into two in the MD direction, two marks were placed on twopoints (point C and point D) at 1 cm and 5 cm from one end,respectively. The test piece was held by a clip at a point between theedge of the piece nearest to the point A and the point A, and the testpiece was suspended in an oven at 150° C. (or 130° C.) such that the MDdirection of the piece was the gravity direction to perform a heattreatment for 30 minutes without a tension. The lengths AB and thelengths CD before and after the heat treatment were measured and thethermal shrinkage ratio (%) was calculated by the following formula.thermal shrinkage ratio (%) in MD direction={(length AB before heattreatment−length AB after heat treatment)/length AB before heattreatment}×100thermal shrinkage ratio (%) in TD direction={(length CD before heattreatment−length CD after heat treatment)/length CD before heattreatment}×100

[Film Resistance (1)]

A separator was cut into a piece having as size of 2.6 cm×2.0 cm, andthe piece was immersed in a methanol solution in which 3% by mass ofnonionic surfactant (EMULGEN 210P, manufactured by Kao Corporation) wasdissolved, followed by air drying. An aluminum foil having a thickness20 μm was cut into a 2.0 cm×1.4 cm piece and a lead tab was attachedthereto. Two pieces of such aluminum foil were prepared, and a separatorwhich was cut out was sandwiched between them so as not to cause a shortcircuit, and the separator was impregnated with 1M LiBF4-propylenecarbonate/ethylene carbonate (mass ratio 1/1) which is an electrolyte.The obtained product was enclosed in an aluminum laminate pack withreduced pressure such that the tab was exposed outside the aluminumpack. Such cells were manufactured such that one, two, or threeseparators were present in the aluminum foil. The cell was placed in athermostat, and the resistance of the cell was measured by analternating current impedance method under conditions of an amplitude of10 mV, and a frequency of 100 kHz at a temperature of 20° C. Themeasured resistance values of the cell were plotted with respect to thenumber of the separators, and the plots were linearly approximated todetermine the slope. The slope was multiplied by the area of anelectrode which is 2.0 cm×1.4 cm to determine the film resistance(ohm·cm²) per one separator.

[Film Resistance (2)]

The separator was impregnated with 1M LiBF4-propylene carbonate/ethylenecarbonate (mass ratio 1/1) as the electrolyte, and the separator wassandwiched by aluminum foil electrodes having a lead tab, and theresulting product was enclosed in an aluminum pack to manufacture a testcell. The resistance (ohm·cm²) of the test cell was measured by analternating current impedance method (measurement frequency: 100 kHz) ata temperature of 20° C.

[Handling Properties (1)]

The handling properties of a separator without an adhesive porous layerwas evaluated by the following method.

When a separator was cut into a 100 mm×100 mm piece by using a stainlessrazor, the existence of a peel of the heat resistant porous layer arounda cutting portion was observed with naked eyes to perform evaluation inaccordance with the following evaluation criteria.

G: Peel was not observed

NG: Peel was observed

[Handling Properties (2)]

The handling properties of a separator with an adhesive porous layer wasevaluated by the following method.

When a separator was conveyed under conditions (conveying speed: 40m/min., unwinding tension: 0.3 N/cm, winding tension: 0.1 N/cm), a peelof an adhesive porous layer was observed with naked eyes to performevaluation in accordance with the following evaluation criteria. As aforeign matter generated by peeling fell off from the separator, amatter fell off from the separator, a matter trapped by the end face ofa winding roll, and a matter observed on the surface of the roll werecounted.

A: No peeling

B: Foreign matters generated by peeling: from one to five per 1000 m²

C: Foreign matters generated by peeling: from six to 20 per 1000 m²

D: Foreign matters generated by peeling: 21 or more per 1000 m²

[Slit Properties]

The slit properties of a separator with an adhesive porous layer wasevaluated by the following method.

While conveying the separator horizontally under the conditions ofconveying speed of 40 m/min., unwinding tension of 0.3 N/cm, and windingtension of 0.1 N/cm, a stainless razor was applied to the separator atan angle of 60° to perform a slit treatment. A chip derived from theadhesive porous layer having a size of 0.5 mm or more is counted withnaked eyes to perform evaluation in accordance with the followingevaluation criteria. A chip fell off from the separator, and a chipobserved on the slit end face were counted.

A: Number of chips having a size of 0.5 mm or more derived from theadhesive porous layer: 5 or less

B: Number of chips having a size of 0.5 mm or more derived from theadhesive porous layer: from 6 to 10

C: Number of chips having a size of 0.5 mm or more derived from theadhesive porous layer: from 11 to 20

D: Number of chips having a size of 0.5 mm or more derived from theadhesive porous layer: 21 or more

[Peel Strength]

A separator with an adhesive porous layer was subjected to a T-peelingtest. Specifically, a separator on both surfaces of which mending tapesmanufactured by 3M Japan Limited were sticked was cut into a 10 mm widthstripe, and ends of the mending tape were drawn at a rate of 20 mm/min.using a tension tester (RTC-1210A, manufactured by ORIENTEC Co., Ltd.),and the stress was measured to create a SS-curve. On the SS-curve,tensions from 10 mm to 40 mm were extracted at a pitch of 0.4 mm and thetensions were averaged. Further, the results for three test pieces wereaveraged, thereby obtaining a peel strength.

[Adhesion to Electrode]

Each of ten test batteries were disassembled and the degree of forceneeded to peel each of a negative electrode and a positive electrodefrom a separator was measured using a tension tester, and 20 measurementvalues in total were averaged. For a separator on only one side of whichan adhesive porous layer was formed, the degree of force needed to peelan electrode which was in contact with the adhesive porous layer fromthe separator was measured, and 10 measurement values in total wereaveraged. Setting the index of the degree of force in Example 101 orExample 201 to 100, the index of each of the Examples and ComparativeExamples was calculated, and evaluation was performed in accordance withthe following evaluation criteria.

A: 60 or more

B: 40 or more but less than 60

C: less than 40

[Cycle Characteristics (Capacity Retention Rate)]

Charge/discharge was repeated for 10 test batteries under theenvironment of 30° C. with charging conditions of constant-current andconstant-voltage charging of 1 C and 4.2V, and discharging conditions ofcutoff constant-current discharging of 1 C, 2.75V. The value obtained bydividing the discharging capacity at the 300-th cycle by the initialcapacity was defined as a capacity retention rate (%), and the averagefor ten test batteries were calculated.

[Oven Test]

Ten test batteries were charged to 4.2 V, and placed in an oven, andthen a 5 kg weight was placed thereon. The oven was set in this statesuch that the temperature of the battery rose at a rate of 2° C./min.,and the temperature of the oven was raised to a temperature of 150° C.,and the change in the voltage of the battery was observed and evaluatedaccording to the following criteria:

G: Almost no change in voltage of battery was observed in all of the 10batteries in a temperature range up to 150° C.

NG: Sharp decrease in voltage of battery was observed at a temperaturearound 150° C. in at least one battery.

[Short Circuit Tests (1) and (2)]

Three or five test batteries were subjected to forced internal shortcircuit test according to JIS C8714 (2007). The results were evaluatedaccording to the following criteria:

—Short circuit test (1): Number of test batteries: 3—

A: No battery fired.

B: One battery fired.

C: Two or three batteries fired.

—Short circuit test (2): Number of test batteries: 5—

AA: No battery fired.

A: One battery fired.

B: Two or 3 batteries fired.

C: Four or five batteries fired.

[Oxidation Resistance]

Ten test batteries were charged at a constant electric current and aconstant voltage of 8 mA/4.3 V at 60° C. for 10 hours. After 100 hourscharging, the batteries were disassembled and the separators werevisually observed and evaluated according to the following evaluationcriteria: Coloring is less likely to occur when the separator has a highoxidation resistance.

G: Coloring was not observed in separator.

NG: Coloring was observed in separator.

First Embodiment of Invention

The separators according to the first embodiment of the presentinvention, and batteries using the separators were produced andperformances of the separators and the batteries were evaluated.

Example 1 Production of Separator

A water-based emulsion containing resin particles having an averageparticle diameter of 250 nm, which particles were a mixture of 70% bymass of polyvinylidene fluoride resin (poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP, molar ratio 95/5) and 30% bymass of an acrylic polymer was provided.

As an inorganic filler, magnesium hydroxide (Mg(OH)₂) having an averageparticle diameter of 880 nm, specific gravity of 2.35 g/cm³, and CPVC of43% by volume was provided.

A water-based emulsion containing the resin particles, magnesiumhydroxide, carboxymethylcellulose (CMC), ion-exchanged water and2-propanol were mixed and the mixture was subjected to dispersiontreatment to obtain a coating liquid having a solid content of 28.4% bymass for forming a heat-resistant porous layer. The coating liquid wasadjusted to attain a ratio of inorganic filler, resin particles and CMCof 94.0/5.0/1.0 and to attain a ratio of ion-exchanged water and2-propanol of 72.7/27.3.

The coating liquid for forming heat resistant porous layer was coated onone side of a polyethylene microporous membrane (film thickness 20 μm,Gurley value 170 sec/100 cc, porosity 43%, flow elongation deformationtemperature of polyethylene of 138.1° C.) using a #6 bar coater, and thecoated liquid was dried at 60° C.

By these operations, a separator in which a heat resistant porous layer,which was an aggregate of the resin particles and the inorganic filler,was formed on one side of the polyethylene microporous membrane wasobtained.

[Production of Test Battery]

—Production of Negative Electrode—

300 g of artificial graphite as a negative electrode active material,7.5 g of a water-soluble dispersion including a modified form of astyrene-butadiene copolymer in an amount of 40% by mass as a binder, 3 gof carboxymethyl cellulose as a thickener, and a proper quantity ofwater were stirred using a double-arm mixer, thereby preparing a slurryfor forming a negative electrode. This slurry for forming a negativeelectrode was coated on a copper foil having a thickness of 10 μm as anegative electrode current collector, and the resulting coated membranewas dried, followed by pressing, to produce a negative electrode havinga negative electrode active material layer.

—Production of Positive Electrode—

89.5 g of lithium cobalt oxide powder as a positive electrode activematerial, 4.5 g of acetylene black as an electrically conductiveadditive, and 6 g of polyvinylidene fluoride as a binder were dissolvedin N-methyl-2-pyrrolidone such that the content of the polyvinylidenefluoride was 6% by mass, and the obtained solution was stirred using adouble-arm mixer, thereby preparing a slurry for forming a positiveelectrode. This slurry for forming a positive electrode was coated on analuminum foil having a thickness of 20 μm as a positive electrodecurrent collector, and the resulting coated membrane was dried, followedby pressing, to produce a positive electrode having a positive electrodeactive material layer.

—Production of Battery—

A lead tab was welded to each of the positive electrode and negativeelectrode. Then, the positive electrode, a separator and the negativeelectrode were stacked in this order to produce a stacked body. Thestacked body was impregnated with an electrolyte, and enclosed in analuminum laminated film pack. Here, 1 M LiPF6-ethylene carbonate/ethylmethyl carbonate (mass ratio: 3/7) was used as the electrolyte. Next,using a vacuum sealer, the inside of the pack was made vacuum, and thepack was tentatively sealed, and, using a heat press machine, thestacked body together with the pack was subjected to a heat pressing,thereby bonding the electrode and the separator and sealing the pack.The heat pressing conditions were 20 kg of load per 1 cm² of theelectrode, a temperature of 90° C., and two minutes of pressing time.

Example 2

A coating liquid having a solid content of 28.4% by mass for forming aheat resistant porous layer was manufactured in the same manner as inExample 1, except that the mass ratio of inorganic filler, resinparticles, and CMC was changed as shown in Table 1.

Equal amounts of the coating liquid for forming heat resistant porouslayer were coated on the both sides of a polyethylene microporousmembrane (film thickness 9 μm, Gurley value 160 sec/100 cc, porosity43%, flow elongation deformation temperature of polyethylene of 140.4°C.) using a #6 bar coater, and the coated liquid was dried at 60° C.

By these operations, a separator in which a heat resistant porous layer,which was an aggregate of the resin particles and the inorganic filler,was formed on the both sides of the polyethylene microporous membranewas obtained. Using this separator, a test battery was manufactured inthe same manner as in Example 1.

Example 3 to 5 and 7 to 9

Separators were obtained by the same manner as in Example 2, except thatthe mass ratios of inorganic filler, resin particles, and CMC in thecoating liquid for forming a heat-resistant porous layer were changed asshown in Table 1, and the amount of the coated liquid was changed asshown in Table 1. Further, using each of the thus obtained separators,test batteries were manufactured by the same manner as in Example 1.

Example 6

A separator was obtained by the same manner as in Example 2, except thatthe mass ratio of inorganic filler, resin particles, and CMC in thecoating liquid for forming a heat-resistant porous layer was changed asshown in Table 1, and the coating liquid was coated on one side of thepolyethylene microporous membrane. Further, using the thus obtainedseparator, a test battery was manufactured by the same manner as inExample 1.

Example 10

A water-based emulsion containing resin particles having an averageparticle diameter of 250 nm, which particles were a mixture of 70% bymass of polyvinylidene fluoride resin (PVDF-HFP, molar ratio 95/5) and30% by mass of an acrylic polymer was provided.

As an inorganic filler, magnesium hydroxide (Mg(OH)₂) having an averageparticle diameter of 880 nm, specific gravity of 2.35 g/cm³, and CPVC of43% by volume was provided.

The water-based emulsion containing the resin particles, the magnesiumhydroxide, CMC and ion-exchanged water were mixed and the mixture wassubjected to dispersion treatment to manufacture a coating liquid havinga solid content of 30.8% by mass for forming heat resistant porouslayer. The coating liquid was adjusted to attain a mass ratio of theinorganic filler, resin particles and CMC of 73.8/25.0/1.2.

Equal amounts of the coating liquid for forming heat resistant porouslayer were coated on the both sides of a polyethylene microporousmembrane (film thickness 9 μm, Gurley value 160 sec/100 cc, porosity43%, flow elongation deformation temperature of polyethylene of 140.4°C.) using a #6 bar coater, and the coated liquid was dried at 60° C.

By these operations, a separator in which a heat resistant porous layer,which was an aggregate of the resin particles and the inorganic filler,was formed on the both sides of the polyethylene microporous membranewas obtained. Using this separator, a test battery was manufactured inthe same manner as in Example 1.

Example 11

A separator was obtained by the same manner as in Example 10, exceptthat the mass ratio of inorganic filler, resin particles, and CMC in thecoating liquid for forming a heat-resistant porous layer was changed asshown in Table 1, the solid content was changed to 31.4% by mass andthat the amount of the coated liquid was changed as shown in Table 1.Further, using the thus obtained separator, a test battery wasmanufactured by the same manner as in Example 1.

Example 12

A water-based emulsion containing resin particles composed ofstyrene-butadiene rubber (SBR) having an average particle diameter of150 nm was provided.

As an inorganic filler, magnesium hydroxide having an average particlediameter of 880 nm, specific gravity of 2.35 g/cm³, and CPVC of 43% byvolume was provided.

The water-based emulsion containing the resin particles, the magnesiumhydroxide, CMC and ion-exchanged water were mixed and the mixture wassubjected to dispersion treatment to manufacture a coating liquid havinga solid content of 28.4% by mass for forming heat resistant porouslayer. The coating liquid was adjusted to attain a mass ratio of theinorganic filler, resin particles and CMC of 94.0/5.0/1.0.

Equal amounts of the coating liquid for forming heat resistant porouslayer were coated on the both sides of a corona treated polyethylenemicroporous membrane (film thickness 9 μm, Gurley value 160 sec/100 cc,porosity 43%, flow elongation deformation temperature of polyethylene of140.4° C.) using a #6 bar coater, and the coated liquid was dried at 60°C.

By these operations, a separator in which a heat resistant porouslayers, which was an aggregate of the resin particles and the inorganicfiller, was formed on the both sides of the polyethylene microporousmembrane was obtained. Using this separator, a test battery wasmanufactured in the same manner as in Example 1.

Example 13

A water-based emulsion containing resin particles having an averageparticle diameter of 250 nm, which particles were a mixture of 70% bymass of polyvinylidene fluoride resin (PVDF-HFP, molar ratio 95/5) and30% by mass of an acrylic polymer was provided.

As an inorganic filler, α-alumina (Al₂O₃) having an average particlediameter of 1.0 μm, specific gravity of 3.95 g/cm³, and CPVC of 58% byvolume was provided.

The water-based emulsion containing the resin particles, the α-alumina,CMC and ion-exchanged water were mixed and the mixture was subjected todispersion treatment to manufacture a coating liquid having a solidcontent of 28.4% by mass for forming a heat resistant porous layer. Thecoating liquid was adjusted to attain a mass ratio of the inorganicfiller, resin particles and CMC of 98.5/1.0/0.5.

Equal amounts of the coating liquid for forming heat resistant porouslayer were coated on the both sides of a corona treated polyethylenemicroporous membrane (film thickness 9 μm, Gurley value 160 sec/100 cc,porosity 43%, flow elongation deformation temperature of polyethylene of140.4° C.) using a #6 bar coater, and the coated liquid was dried at 60°C.

By these operations, a separator in which a heat resistant porous layer,which was an aggregate of the resin particles and the inorganic filler,was formed on the both sides of the polyethylene microporous membranewas obtained. Using this separator, a test battery was manufactured inthe same manner as in Example 1.

Example 14

A separator was obtained by the same manner as in Example 13, exceptthat the α-alumina was replaced with magnesium oxide (MgO) (averageparticle diameter of 1.0 μm, specific gravity of 3.58 g/cm³, and CPVC of50% by volume), the mass ratio of inorganic filler, resin particles, andCMC in the coating liquid for forming a heat-resistant porous layer waschanged as shown in Table 1, and that the amount of the coated liquidwas changed as shown in Table 1. Further, using the thus obtainedseparator, a test battery was manufactured by the same manner as inExample 1.

Example 15

A separator was obtained by the same manner as in Example 13, exceptthat the α-alumina was replaced with aluminum hydroxide (Al(OH)₃)(average particle diameter of 1.0 μm, specific gravity of 2.42 g/cm³,and CPVC of 48% by volume), the mass ratio of inorganic filler, resinparticles, and CMC in the coating liquid for forming a heat-resistantporous layer was changed as shown in Table 1, and that the amount of thecoated liquid was changed as shown in Table 1. Further, using the thusobtained separator, a test battery was manufactured by the same manneras in Example 1.

Example 16

A separator was obtained by the same manner as in Example 13, exceptthat the α-alumina was replaced with kaolin (Al₄Si₄O₁₀(OH)₈) (averageparticle diameter of 1.0 μm, specific gravity of 2.60 g/cm³, and CPVC of46% by volume), the mass ratio of inorganic filler, resin particles, andCMC in the coating liquid for forming a heat-resistant porous layer waschanged as shown in Table 1, and that the amount of the coated liquidwas changed as shown in Table 1. Further, using the thus obtainedseparator, a test battery was manufactured by the same manner as inExample 1.

Comparative Example 1

A separator was obtained by the same manner as in Example 2, except thatthe mass ratio of inorganic filler, resin particles, and CMC in thecoating liquid for forming a heat-resistant porous layer were changed asshown in Table 1, the solid content was changed to 26.3% by mass andthat the amount of the coated liquid was changed as shown in Table 1.Further, using the thus obtained separator, a test battery wasmanufactured by the same manner as in Example 1.

Comparative Example 2

A separator was obtained by the same manner as in Example 2, except thatthe mass ratio of inorganic filler, resin particles, and CMC in thecoating liquid for forming a heat-resistant porous layer was changed asshown in Table 1, the solid content was changed to 35.3% by mass andthat the amount of the coated liquid was changed as shown in Table 1.Further, using the thus obtained separator, a test battery wasmanufactured by the same manner as in Example 1.

Comparative Example 3

A water-based emulsion containing resin particles having an averageparticle diameter of 250 nm, which particles were a mixture of 70% bymass of polyvinylidene fluoride resin (PVDF-HFP, molar ratio 95/5) and30% by mass of an acrylic polymer was provided. Further, polyethyleneparticles (CHEMIPEARL W100 manufactured by MITSUI CHEMICALS, INC.,average particle diameter 3 μm) was provided.

As an inorganic filler, magnesium hydroxide (Mg(OH)₂) having an averageparticle diameter of 880 nm, specific gravity of 2.35 g/cm³, and CPVC of43% by volume was provided.

The water-based emulsion containing the resin particles, polyethyleneparticles including the polyvinylidene fluoride resin, magnesiumhydroxide, CMC and ion-exchanged water were mixed and the mixture wassubjected to dispersion treatment to manufacture a coating liquid havinga solid content of 30.8% by mass for forming a heat resistant porouslayer. The coating liquid was adjusted to attain a mass ratio of theinorganic filler, resin particles containing polyvinylidene fluorideresin, polyethylene particles and CMC of 54.5/3.6/36.4/5.5.

Equal amount of the coating liquid for forming heat resistant porouslayer was coated on the both sides of a polyethylene microporousmembrane (film thickness 9 μm, Gurley value 160 sec/100 cc, porosity43%, flow elongation deformation temperature of polyethylene of 140.4°C.) using a #6 bar coater, and the coated liquid was dried at 60° C.

By these operations, a separator in which a heat resistant porous layer,which was an aggregate of the resin particles and the inorganic filler,was formed on the both sides of the polyethylene microporous membranewas obtained. Using this separator, a test battery was manufactured inthe same manner as in Example 1.

The characteristics and evaluation results of the separators and thetest batteries of Examples 1 to 16 and Comparative Examples 1 to 3 areshown in Table 1 and Table 2.

TABLE 1 Composition of heat resistant porous layer Material of heatresistant porous layer [mass %] Resin Inorganic CPVC Inorganic Resinparticles filler [vol %] Others filler particles Others Example 1  PVDFMg(OH)₂ 43 CMC 94.0 5.0 1.0 Example 2  PVDF Mg(OH)₂ 43 CMC 83.7 15.0 1.3Example 3  PVDF Mg(OH)₂ 43 CMC 88.7 10.0 1.3 Example 4  PVDF Mg(OH)₂ 43CMC 93.7 5.0 1.3 Example 5  PVDF Mg(OH)₂ 43 CMC 94.0 5.0 1.0 Example 6 PVDF Mg(OH)₂ 43 CMC 94.0 5.0 1.0 Example 7  PVDF Mg(OH)₂ 43 CMC 94.2 5.00.8 Example 8  PVDF Mg(OH)₂ 43 CMC 97.0 2.0 1.0 Example 9  PVDF Mg(OH)₂43 CMC 98.0 1.0 1.0 Example 10 PVDF Mg(OH)₂ 43 CMC 73.8 25.0 1.2 Example11 PVDF Mg(OH)₂ 43 CMC 80.4 18.4 1.2 Example 12 SBR Mg(OH)₂ 43 CMC 94.05.0 1.0 Example 13 PVDF alumina 58 CMC 98.5 1.0 0.5 Example 14 PVDF MgO50 CMC 94.0 5.0 1.0 Example 15 PVDF Al(OH)₃ 48 CMC 94.0 5.0 1.0 Example16 PVDF kaolin 46 CMC 94.0 5.0 1.0 Comparative PVDF Mg(OH)₂ 43 CMC 78.420.4 1.2 Example 2 Comparative PVDF, Mg(OH)₂ 43 CMC 54.5 40.0 5.5Example 3 PE Heat resistant porous layer Amount of coated InorganicThickness liquid filler Porosity × Provided (total) (dry weight) contentPorosity Vf Vf/ Vf/CPVC on [μm] [g/m²] [g/m²] [%] [vol %] CPVC [%]Example 1  one side 12.1 9.5 8.9 65 31.4 0.73 47 Example 2  both sides9.1 8.5 7.1 57 33.3 0.77 44 Example 3  both sides 13.8 12.1 10.7 60 33.10.77 46 Example 4  both sides 10.1 8.8 8.2 61 34.7 0.81 49 Example 5 both sides 12.2 10.5 9.8 62 34.4 0.80 50 Example 6  one side 7.6 5.6 5.367 29.5 0.69 46 Example 7  both sides 9.4 8.3 7.8 61 35.4 0.82 50Example 8  both sides 11.4 9.7 9.4 62 35.1 0.82 51 Example 9  both sides13.3 11.0 10.8 64 34.5 0.80 51 Example 10 both sides 7.0 9.2 6.8 45 41.30.96 43 Example 11 both sides 7.0 7.7 6.2 52 37.6 0.88 46 Example 12both sides 12.2 10.4 9.8 60 34.1 0.79 47 Example 13 both sides 11.6 18.918.6 57 40.6 0.70 40 Example 14 both sides 12.1 15.5 14.6 60 33.6 0.6740 Example 15 both sides 12.0 10.7 10.1 61 34.6 0.72 44 Example 16 bothsides 12.4 10.9 10.2 64 31.8 0.69 44 Comparative both sides 3.4 4.6 3.637 45.1 1.05 39 Example 2 Comparative both sides 5.0 5.4 2.9 20 25.00.58 12 Example 3

TABLE 2 Gurley Film Thermal dimensional Thermal shrinkage Handling Cyclevalue resistance (1) change [%] (150° C.) [%] properties Oxidation Ovencharacteristics [sec/100 cc] [ohm · cm²] MD TD MD TD (1) resistance test[%] Example 1  270 5.58 0.2 0.2 2.2 2.3 G G G 75 Example 2  321 7.37 0.10.2 2.3 1.8 G G G 72 Example 3  253 5.85 0 0.1 1.1 1.0 G G G 75 Example4  198 3.77 0 0.1 2.4 2.0 G G G 83 Example 5  193 3.84 0 0.2 3.0 2.8 G GG 81 Example 6  161 3.57 0.8 0.2 2.7 2.0 G G G 84 Example 7  187 3.570.1 0.2 2.9 2.3 G G G 84 Example 8  181 3.35 0 0.3 2.5 1.8 G G G 85Example 9  180 3.39 0 0.2 2.6 3.0 G G G 85 Example 10 398 7.81 0.1 0.32.2 1.7 G G G 70 Example 11 227 7.54 0.1 0.4 2.9 2.5 G G G 72 Example 12195 3.70 0.1 0.2 2.5 2.1 G NG G 70 Example 13 208 3.39 0 0.2 2.6 3.0 G GG 85 Example 14 195 3.57 0.1 0.2 2.9 2.3 G G G 84 Example 15 203 3.35 00.3 2.5 1.8 G G G 86 Example 16 210 3.39 0 0.2 2.6 3.0 G G G 85Comparative 895 11.20 3.1 4.8 8.9 19.9 G G NG 51 Example 1  Comparative316 9.03 0.1 0.2 2.3 1.8 NG G G 63 Example 2  Comparative 165 4.69 4.710.1 32.5 25.0 G NG NG 69 Example 3 

From the results shown in Table 2, it can be seen that the separators ofExamples 1 to 6 are excellent in ion permeability and thermaldimensional stability, and that the test batteries manufactured by usingthe separators of Examples 1 to 6 are excellent in batterycharacteristics and safety.

With regard to the separators of Example 1 to Example 16, the moisturecontents were measured by the following method.

The moisture was vaporized from each separator at 120° C. by using amoisture vaporizing device (model VA-100, manufactured by MitsubishiChemical Analytech, Co., Ltd.) and thereafter, the moisture content wasmeasured using a Karl Fischer moisture meter (CA-100, manufactured byMitsubishi Chemical Co., Ltd.). As a result, all the moisture contentsof the separators of Example 1 to Example 16 were 1,000 ppm or less.

Second Embodiment of the Present Invention (1)

Separators according to the second embodiment of the present inventionand batteries using these separators were manufactured, and theperformances of the separators and the batteries were evaluated.

Example 101 Manufacturing of Separators

—Forming of Heat Resistant Porous Layer—

A water-based emulsion containing resin particles having an averageparticle diameter of 250 nm, which particles were a mixture of 70% bymass of polyvinylidene fluoride resin (PVDF-HFP, molar ratio 95/5) and30% by mass of an acrylic polymer was provided.

As an inorganic filler, magnesium hydroxide (Mg(OH)₂) having an averageparticle diameter of 880 nm, specific gravity of 2.35 g/cm³, and CPVC of43% by volume was provided.

The magnesium hydroxide was dispersed in the water-based emulsioncontaining the resin particles to manufacture a coating liquid forforming heat resistant porous layer. The coating liquid was adjusted toattain a resin concentration of 7.4% by mass and to attain a ratio ofthe filler to the total of the resin and the filler of 90% by mass.

Equal amounts of the coating liquid for forming heat resistant porouslayer were coated on the both sides of a polyethylene microporousmembrane (film thickness 9 Gurley value 160 sec/100 cc, porosity 43%,flow elongation deformation temperature of polyethylene of 140.4° C.)using a bar coater, and the coated liquid was dried at 60° C.

By these operations, a stacked body in which a heat resistant porouslayer, which was an aggregate of the resin particles and the inorganicfiller, was formed on the both sides of the polyethylene microporousmembrane was obtained.

—Forming of Adhesive Porous Layer—

A polyvinylidene fluoride resin (PVDF-HFP, molar ratio 97/3,weight-average molecular weight 1,000,000) was provided.

PVDF-HFP was dissolved in a mixed solvent of dimethylacetamide andtripropylene glycol (dimethylacetamide/tripropylene glycol=7/3 [massratio]) to a concentration of 5% by mass to manufacture a coating liquidfor forming adhesive porous layer.

Equal amounts of the obtained coating liquid for forming adhesive porouslayer were coated on the both sides of the stacked body and theresultant was immersed in a coagulating liquid(water/dimethylacetamide/tripropylene glycol=57/30/13 [mass ratio]) at40° C. to solidify the coating liquid. The resultant was then washedwith water and dried.

By these operations, a separator in which an adhesive porous layercomposed of PVDF-HFP was formed on the both sides of the stacked body,was obtained.

[Manufacturing of Test Battery]

[Production of Test Battery]

—Production of Negative Electrode—

300 g of artificial graphite as a negative electrode active material,7.5 g of a water-soluble dispersion including a modified form of astyrene-butadiene copolymer in an amount of 40% by mass as a binder, 3 gof carboxymethyl cellulose as a thickener, and a proper quantity ofwater were stirred using a double-arm mixer, thereby preparing a slurryfor forming a negative electrode. This slurry for forming a negativeelectrode was coated on a copper foil having a thickness of 10 μm as anegative electrode current collector, and the resulting coated membranewas dried, followed by pressing, to produce a negative electrode havinga negative electrode active material layer.

—Production of Positive Electrode—

89.5 g of lithium cobalt oxide powder as a positive electrode activematerial, 4.5 g of acetylene black as an electrically conductiveadditive, and 6 g of polyvinylidene fluoride as a binder were dissolvedin N-methyl-2-pyrrolidone such that the content of the polyvinylidenefluoride was 6% by mass, and the obtained solution was stirred using adouble-arm mixer, thereby preparing a slurry for forming a positiveelectrode. This slurry for forming a positive electrode was coated on analuminum foil having a thickness of 20 μm as a positive electrodecurrent collector, and the resulting coated membrane was dried, followedby pressing, to produce a positive electrode having a positive electrodeactive material layer.

—Production of Battery—

A lead tab was welded to each of the positive electrode and negativeelectrode. Then, the positive electrode, a separator and the negativeelectrode were stacked in this order to produce a stacked body. Thestacked body was impregnated with an electrolyte, and enclosed in analuminum laminated film pack. Here, 1 M LiPF₆-ethylene carbonate/ethylmethyl carbonate (mass ratio: 3/7) was used as the electrolyte. Nextusing a vacuum sealer, the inside of the pack was made vacuum and thepack was tentatively sealed, and, using a heat press machine, thestacked body together with the pack was subjected to a heat pressing,thereby bonding the electrode and the separator and sealing the pack.The heat pressing conditions were 20 kg of load per 1 cm² of theelectrode, a temperature of 90° C., and two minutes of pressing time.

Examples 102 to 104

Separators were obtained by the same manner as in Example 101, exceptthat the ratio of the filler to the total of the resin and the filler inthe coating liquid for forming heat resistant porous layer was changedas shown in Table 3. Using the separators, test batteries weremanufactured by the same manner as in Example 101.

Example 105

A separator was obtained by the same manner as in Example 101, exceptthat the coating liquid was coated on one side of the polyethylenemicroporous membrane. Further, using the thus obtained separator, a testbattery was manufactured by the same manner as in Example 101.

Example 106

A separator was obtained by the same manner as in Example 104, exceptthat the coating liquid was coated on one side of the polyethylenemicroporous membrane. Further, using the thus obtained separator, a testbattery was manufactured by the same manner as in Example 101.

Example 107 Forming of Heat Resistant Porous Layer

A water-based emulsion containing resin particles composed ofstyrene-butadiene rubber (SBR) having an average particle diameter of150 nm was provided.

As an inorganic filler, magnesium hydroxide (Mg(OH)₂) having an averageparticle diameter of 880 nm, specific gravity of 2.35 g/cm³, and CPVC of43% by volume was provided.

The magnesium hydroxide was dispersed in the water-based emulsioncontaining the SBR to manufacture a coating liquid for forming a heatresistant porous layer. The coating liquid was adjusted to attain an SBRconcentration of 7.4% by mass and to attain a ratio of the filler to thetotal of the resin and the filler of 70% by mass.

Equal amounts of the coating liquid for forming heat resistant porouslayer were coated on the both sides of a polyethylene microporousmembrane (film thickness 9 Gurley value 160 sec/100 cc, porosity 43%,flow elongation deformation temperature of polyethylene of 140.4° C.)using a bar coater, and the coated liquid was dried at 60° C.

By these operations, a stacked body in which a heat resistant porouslayer, which was an aggregate of the resin particles and the inorganicfiller, was formed on the both sides of the polyethylene microporousmembrane was obtained.

An adhesive porous layer was formed on both sides of the stacked body bythe same manner as in Example 101 to obtain a separator. Further, usingthe thus obtained separator, a test battery was manufactured by the samemanner as in Example 101.

Example 108

A separator was obtained by the same manner as in Example 107, exceptthat the SBR concentration in the coating liquid for forming a heatresistant porous layer was changed to 5.0% by mass, the ratio of thefiller to the total of the resin and the filler was changed to 80% bymass, and that the coating liquid was coated on one side of thepolyethylene microporous membrane. Further, using the thus obtainedseparator, a test battery was manufactured by the same manner as inExample 101.

Example 109 Forming of Heat Resistant Porous Layer

A polyvinylidene fluoride resin (PVDF-HFP, molar ratio 97/3,weight-average molecular weight 1,000,000) was provided.

As a filler, magnesium hydroxide (Mg(OH)₂) having an average particlediameter of 880 nm, specific gravity of 2.35 g/cm³, and CPVC of 43% byvolume was provided.

PVDF-HFP was dissolved in a mixed solvent of dimethylacetamide andtripropylene glycol (dimethylacetamide/tripropylene glycol=7/3 [massratio]) to a concentration of 5% by mass to manufacture a coating liquidfor forming an adhesive porous layer. The coating liquid was adjusted toattain a ratio of the filler to the total of the resin and the filler of90% by mass.

Equal amounts of the coating liquid for forming a heat resistant porouslayer were coated on the both sides of a polyethylene microporousmembrane (film thickness 9 μm, Gurley value 160 sec/100 cc, porosity43%, flow elongation deformation temperature of polyethylene of 140.4°C.), and the resultant was immersed in a coagulating liquid(water/dimethylacetamide/tripropylene glycol=57/30/13 [mass ratio]) at40° C. to solidify the coating liquid. The resultant was then washedwith water and dried.

By these operations, a stacked body in which a heat resistant porouslayer, which was an aggregate of the resin particles and the inorganicfiller, was formed on the both sides of the polyethylene microporousmembrane was obtained.

An adhesive porous layer was formed on both sides of the stacked body bythe same manner as in Example 101 to obtain a separator. Further, usingthe thus obtained separator, a test battery was manufactured by the samemanner as in Example 101.

Example 110

A separator was obtained by the same manner as in Example 109, exceptthat PVDF-HFP was replaced with poly(vinylidene fluoride) (PVDF, weightaverage molecular weight of 1,000,000), and the ratio of the filler tothe total of the resin and the filler was changed to 80% by mass.Further, using the thus obtained separator, a test battery wasmanufactured by the same manner as in Example 101.

Example 111 Forming of Heat Resistant Porous Layer

An aqueous solution containing polyvinyl alcohol (PVA) having asaponification value of 98 or more and an average polymerization degreeof 2400 was provided.

As a filler, magnesium hydroxide (Mg(OH)₂) having an average particlediameter of 880 nm, specific gravity of 2.35 g/cm³, and CPVC of 43% byvolume was provided.

The magnesium hydroxide was dispersed in the water-based emulsioncontaining the PVA to manufacture a coating liquid for forming a heatresistant porous layer. The coating liquid was adjusted to attain a PVAconcentration of 7.4% by mass and to attain a ratio of the filler to thetotal of the resin and the filler of 70% by mass.

Equal amounts of the coating liquid for forming a heat resistant porouslayer were coated on the both sides of a polyethylene microporousmembrane (film thickness 9 μm, Gurley value 160 sec/100 cc, porosity43%, flow elongation deformation temperature of polyethylene of 140.4°C.) using a bar coater, and the coated liquid was dried at 60° C.

By these operations, a stacked body in which a heat resistant porouslayer containing the resin and the filler was formed on the both sidesof the polyethylene microporous membrane was obtained.

An adhesive porous layers was formed on both sides of the stacked bodyby the same manner as in Example 101 to obtain a separator. Further,using the thus obtained separator, a test battery was manufactured bythe same manner as in Example 101.

Example 112

A separator was obtained by the same manner as in Example 101, exceptthat the magnesium hydroxide was replaced with α-alumina (Al₂O₃) havingan average particle diameter of 1.0 μm, specific gravity of 3.95 g/cm³,and CPVC of 58% by volume), and the ratio of the filler to the total ofthe resin and the filler was changed to 65% by mass. Further, using thethus obtained separator, a test battery was manufactured by the samemanner as in Example 101.

Example 113

A separator was obtained by the same manner as in Example 101, exceptthat the magnesium hydroxide was replaced with magnesium oxide (MgO)(average particle diameter of 1.0 μm, specific gravity of 3.58 g/cm³,and CPVC of 50% by volume), and the ratio of the filler to the total ofthe resin and the filler was changed to 70% by mass. Further, using thethus obtained separator, a test battery was manufactured by the samemanner as in Example 101.

Example 114

A separator was obtained by the same manner as in Example 101, exceptthat the magnesium hydroxide was replaced with aluminum hydroxide(Al(OH)₃) (average particle diameter of 1.0 μm, specific gravity of 2.42g/cm³, and CPVC of 48% by volume), and the ratio of the filler to thetotal of the resin and the filler was changed to 86% by mass. Further,using the thus obtained separator, a test battery was manufactured bythe same manner as in Example 101.

Example 115

A separator was obtained by the same manner as in Example 101, exceptthat the magnesium hydroxide was replaced with kaolin (Al₄Si₄O₁₀(OH)₈)(average particle diameter of 1.0 μm, specific gravity of 2.60 g/cm³,and CPVC of 46% by volume), and the ratio of the filler to the total ofthe resin and the filler was changed to 50% by mass. Further, using thethus obtained separator, a test battery was manufactured by the samemanner as in Example 101.

Example 116

A separator was obtained by the same manner as in Example 101, exceptthat the magnesium hydroxide was replaced with talc (Mg₃Si₄O₁₀(OH)₂)(average particle diameter of 1.0 μm, specific gravity of 2.70 g/cm³,CPVC of 51% by volume), and the ratio of the filler to the total of theresin and the filler was changed to 50% by mass. Further, using the thusobtained separator, a test battery was manufactured by the same manneras in Example 101.

Example 117

A separator was obtained by the same manner as in Example 101, exceptthat the magnesium hydroxide was replaced with plate boehmite(Al₂O₃.H₂O) (average particle diameter of 1.2 μm, specific gravity of2.70 g/cm³, CPVC of 26% by volume), and the ratio of the filler to thetotal of the resin and the filler was changed to 50% by mass. Further,using the thus obtained separator, a test battery was manufactured bythe same manner as in Example 101.

Example 118

A separator was obtained by the same manner as in Example 101, exceptthat the magnesium hydroxide was replaced with plate calcium carbonate(CaCO₃) (average particle diameter of 1.1 μm, specific gravity of 2.60g/cm³, CPVC of 24% by volume), and the ratio of the filler to the totalof the resin and the filler was changed to 50% by mass. Further, usingthe thus obtained separator, a test battery was manufactured by the samemanner as in Example 101.

Example 119 Forming of Heat Resistant Porous Layer

An aqueous solution containing polyvinyl alcohol (PVA) having asaponification value of 98 or more and an average polymerization degreeof 2400 was provided.

As a filler, plate calcium carbonate (CaCO₃) (average particle diameterof 1.1 μm, specific gravity of 2.60 g/cm³, CPVC of 24% by volume) wasprovided.

The plate calcium carbonate was dispersed in the water-based emulsioncontaining the PVA to manufacture a coating liquid for forming a heatresistant porous layer. The coating liquid was adjusted to attain a PVAconcentration of 7.4% by mass and to attain a ratio of the filler to thetotal of the resin and the filler of 80% by mass.

Equal amounts of the coating liquid for forming heat resistant porouslayer were coated on the both sides of a polyethylene microporousmembrane (film thickness 9 μm, Gurley value 160 sec/100 cc, porosity43%, flow elongation deformation temperature of polyethylene of 140.4°C.) using a bar coater, and the coated liquid was dried at 60° C.

By these operations, a stacked body including heat resistant porouslayers containing the resin and the filler, which heat resistant porouslayers were formed on the both sides of the polyethylene microporousmembrane was obtained.

An adhesive porous layer was formed on both sides of the stacked body bythe same manner as in Example 101 to obtain a separator. Further, usingthe thus obtained separator, a test battery was manufactured by the samemanner as in Example 101.

Example 120

A separator was obtained by the same manner as in Example 101, exceptthat poly(methyl methacrylate) (PMMA) resin having an average particlediameter of 1.8 μm was dispersed to a concentration of 2.1% by mass.Further, using the thus obtained separator, a test battery wasmanufactured by the same manner as in Example 101.

Example 121

A separator was obtained by the same manner as in Example 103, exceptthat adhesive porous layers were formed by using a water-based emulsioncontaining resin particles of styrene-butadiene rubber (SBR) (averageparticle diameter of 150 nm) at a concentration of 5.0% by mass as thecoating liquid for forming an adhesive porous layer, and by drying thecoating liquid after coating. Further, using the thus obtainedseparator, a test battery was manufactured by the same manner as inExample 101.

Comparative Example 101

A separator was obtained by the same manner as in Example 101, exceptthat the ratio of the filler to the total of the resin and the filler inthe coating liquid for forming a heat resistant porous layer was changedto 70% by mass, and the adhesive porous layer was formed on one side.Further, using the thus obtained separator, a test battery wasmanufactured by the same manner as in Example 101.

Comparative Example 102

A separator was obtained by the same manner as in Example 101, exceptthat the ratio of the filler to the total of the resin and the filler inthe coating liquid for forming heat resistant porous layer was changedto 50% by mass, and the adhesive porous layer was formed on one side.Further, using the thus obtained separator, a test battery wasmanufactured by the same manner as in Example 101.

Comparative Example 103

A separator was obtained by the same manner as in Example 101, exceptthat the heat resistant porous layers were not formed and the thicknessof the adhesive porous layers were changed. Further, using the thusobtained separator, a test battery was manufactured by the same manneras in Example 101.

Comparative Example 104

A separator was obtained by the same manner as in Example 101, exceptthat the ratio of the filler to the total of the resin and the filler inthe coating liquid for forming heat resistant porous layer was changedto 99% by mass. Further, using the thus obtained separator, a testbattery was manufactured by the same manner as in Example 101.

Comparative Example 105

A separator was obtained by the same manner as in Example 101, exceptthat the concentration of the resin was changed to 7.0% by mass and theratio of the filler to the total of the resin and the filler in thecoating liquid for forming heat resistant porous layer was changed to50% by mass. Further, using the thus obtained separator, a test batterywas manufactured by the same manner as in Example 101.

Comparative Example 106

A separator was obtained by the same manner as in Example 101, exceptthat a mixture of two types of magnesium hydroxide (a mixture obtainedby mixing magnesium hydroxide having an average particle diameter of 0.8μm and magnesium hydroxide having an average particle diameter of 0.2 μmat a mass ratio of 1:1, specific gravity of 2.36 g/cm³, CPVC of 80% byvolume) was used, and the ratio of the filler to the total of the resinand the filler in the coating liquid for forming a heat resistant porouslayer was changed to 50% by mass. Further, using the thus obtainedseparator, a test battery was manufactured by the same manner as inExample 101.

The characteristics and evaluation results of the separators and thetest batteries of Examples 101 to 121 and Comparative Examples 101 to106 are shown in Table 3 and Table 4.

TABLE 3 PVDF Heat resistant porous layer Ratio of filler to totalMaterial of heat resistant porous layer Thickness of resin and CPVCProvided (total) filler Resin Filler [vol %] on [μm] [mass %] Example101 PVDF particles Mg(OH)₂ 43 both sides 5 90 Example 102 PVDF particlesMg(OH)₂ 43 both sides 5 80 Example 103 PVDF particles Mg(OH)₂ 43 bothsides 5 70 Example 104 PVDF particles Mg(OH)₂ 43 both sides 5 50 Example105 PVDF particles Mg(OH)₂ 43 one side 3 90 Example 106 PVDF particlesMg(OH)₂ 43 one side 3 50 Example 107 SBR particles Mg(OH)₂ 43 both sides3 70 Example 108 SBR particles Mg(OH)₂ 43 one side 3 80 Example 109PVDF-HFP Mg(OH)₂ 43 both sides 5 90 Example 110 PVDF Mg(OH)₂ 43 bothsides 5 80 Example 111 PVA Mg(OH)₂ 43 both sides 3 70 Example 112 PVDFparticles alumina 58 both sides 3 65 Example 113 PVDF particles MgO 50both sides 3 70 Example 114 PVDF particles Al(OH)₃ 48 both sides 3 86Example 115 PVDF particles kaolin 46 both sides 5 50 Example 116 PVDFparticles talc 51 both sides 5 80 Example 117 PVDF particles plate 26both sides 5 50 boehmite Example 118 PVDF particles plate 24 both sides5 50 CaCO₃ Example 119 PVA plate 24 both sides 5 80 CaCO₃ Example 120PVDF particles Mg(OH)₂ 43 both sides 5 90 Example 121 PVDF particlesMg(OH)₂ 43 both sides 5 70 Comparative PVDF particles Mg(OH)₂ 43 bothsides 5 70 Example 101 Comparative PVDF particles Mg(OH)₂ 43 both sides5 50 Example 102 Comparative — — — — — — Example 103 Comparative PVDFparticles Mg(OH)₂ 43 both sides 5 99 Example 104 Comparative PVDFparticles Mg(OH)₂ 43 both sides 5 50 Example 105 Comparative PVDFparticles Mg(OH)₂ 80 both sides 5 50 Example 106 Adhesive porous layerHeat resistant porous layer Thickness Porosity Vf Vf/ Provided (total)Porosity [%] [vol %] CPVC on Resin Filler [μm] [%] Example 101 54 400.93 both PVDF- — 2 40 sides HFP Example 102 60 30 0.70 both PVDF- — 240 sides HFP Example 103 66 22 0.51 both PVDF- — 2 40 sides HFP Example104 60 17 0.40 both PVDF- — 2 40 sides HFP Example 105 54 40 0.93 bothPVDF- — 2 40 sides HFP Example 106 60 17 0.40 both PVDF- — 2 40 sidesHFP Example 107 56 22 0.51 both PVDF- — 2 40 sides HFP Example 108 56 340.79 both PVDF- — 2 40 sides HFP Example 109 63 30 0.70 both PVDF- — 240 sides HFP Example 110 50 21 0.49 both PVDF- — 2 40 sides HFP Example111 61 22 0.51 both PVDF- — 2 40 sides HFP Example 112 36 29 0.50 bothPVDF- — 2 40 sides HFP Example 113 53 25 0.50 both PVDF- — 2 40 sidesHFP Example 114 74 21 0.44 both PVDF- — 2 65 sides HFP Example 115 44 230.50 both PVDF- — 2 40 sides HFP Example 116 32 49 0.96 both PVDF- — 240 sides HFP Example 117 54 18 0.69 both PVDF- — 2 40 sides HFP Example118 76 10 0.42 both PVDF- — 2 40 sides HFP Example 119 78 22 0.92 bothPVDF- — 2 40 sides HFP Example 120 54 40 0.93 both PVDF- PMMA 3 55 sidesHFP Example 121 66 22 0.51 both SRR — 2 44 sides particles Comparative53 30 0.70 one PVDF- — 1 40 Example 101 side HFP Comparative 50 22 0.51one PVDF- — 2 40 Example 102 side HFP Comparative — — — both PVDF- — 539 Example 103 sides HFP Comparative 57 43 1.00 both PVDF- — 2 40Example 104 sides HFP Comparative 62 16 0.37 both PVDF- — 2 40 Example105 sides HFP Comparative 35 28 0.35 both PVDF- — 2 40 Example 106 sidesHFP

TABLE 4 Average Film Short Short porosity of Gurley resistance Thermalshrinkage Peel Adhesion circuit circuit Cycle Thickness coating layervalue (2) (MD direction) [%] strength to test test characteristics [μm][%] [sec/100 cc] [ohm · cm²] 150° C. 130° C. [N/cm] electrode (1) (2)[%] Example 101 16 50 340 3.2 6.2 4.7 0.07 A A AA 90 Example 102 16 54356 3.3 7.6 3.8 0.08 A A AA 89 Example 103 16 59 375 3.4 11.3 5.7 0.13 AA AA 89 Example 104 16 54 356 3.3 17.0 8.5 0.20 A A AA 89 Example 105 1448 444 3.8 9.0 4.7 0.12 A A AA 85 Example 106 14 52 476 4.0 17.0 8.40.23 A A AA 79 Example 107 14 50 454 3.9 11.3 5.8 0.05 A A A 81 Example108 14 50 330 3.4 13.0 6.6 0.06 A — A 82 Example 109 16 56 335 3.3 10.25.0 0.07 A A AA 88 Example 110 16 47 340 3.2 8.0 4.1 0.07 A — AA 85Example 111 14 53 481 4.0 11.3 5.6 0.18 A A AA 80 Example 112 14 38 3934.2 11.3 5.8 0.25 A A AA 76 Example 113 14 48 441 3.8 11.3 5.7 0.20 A AAA 77 Example 114 14 70 490 4.2 13.2 8.4 0.07 B A AA 74 Example 115 1643 307 3.0 12.2 5.7 0.24 A — AA 89 Example 116 16 34 206 4.2 8.1 3.80.18 A — AA 75 Example 117 16 50 338 3.5 2.8 0.5 0.15 A — AA 83 Example118 16 66 405 4.1 5.1 1.3 0.07 A — AA 78 Example 119 16 67 358 3.3 8.43.5 0.06 A — AA 85 Example 120 17 54 337 3.2 6.1 4.7 0.04 B A AA 90Example 121 16 60 375 3.4 11.3 5.8 0.11 A A AA 87 Comparative 15 51 3343.2 9.4 4.0 0.16 C C B 70 Example 101 Comparative 16 47 326 3.1 11.0 5.70.20 C — A 89 Example 102 Comparative 14 39 320 3.1 not 50.0 0.15 A C C85 Example 103 measureable Comparative 16 52 282 3.5 2.0 0.0 0.02 B B A72 Example 104 Comparative 16 56 362 3.6 30.0 13.0 0.14 A B B 78 Example105 Comparative 16 36 362 3.6 21.0 9.4 0.25 A — C 80 Example 106

From the results shown in Table 4, it can be seen that the separators ofExamples 101 to 121 are excellent in ion permeability and thermaldimensional stability, and that the test batteries manufactured by usingthe separators of Examples 101 to 121 are excellent in batterycharacteristics and safety.

Second Embodiment of Invention (2)

Separators according to the second embodiment of the present inventionand batteries using these separators were manufactured, and theperformances of the separators and the batteries were evaluated.

Example 201 Manufacturing of Separators

—Forming of Heat Resistant Porous Layer—

A water-based emulsion containing resin particles having an averageparticle diameter of 250 nm, which particles were a mixture of 70% bymass of polyvinylidene fluoride-resin (PVDF-HFP, molar ratio 95/5) and30% by mass of an acrylic polymer was provided.

As a filler, magnesium hydroxide (Mg(OH)₂) having an average particlediameter of 880 nm, specific gravity of 2.35 g/cm³, and CPVC of 43% byvolume was provided.

The water-based emulsion containing the resin particles, magnesiumhydroxide, carboxymethylcellulose (CMC) and ion-exchanged water weremixed and the mixture was subjected to dispersion treatment tomanufacture a coating liquid having a solid content of 24.8% by mass forforming a heat resistant porous layer. The coating liquid was adjustedto attain a mass ratio of the filler, resin particles and CMC of96.0/3.0/1.0.

The coating liquid for forming heat resistant porous layer was coated onone side of a corona treated polyethylene microporous membrane (filmthickness 9 μm, Gurley value 183 sec/100 cc, porosity 36%, flowelongation deformation temperature of polyethylene of 132.4° C.) using agravure coater, and the coated liquid was dried at 60° C.

By these operations, a separator including a heat resistant porous layerwhich was an aggregate of the resin particles and the inorganic fillerwas formed on one side of the polyethylene microporous membrane wasobtained.

—Forming of Adhesive Porous Layer—

PVDF-HFP having a polymerization ratio (molar ratio) of 98.9/1.1 and aweight average molecular weight of 1,950,000 was mixed with PVDF-HFPhaving a polymerization ratio (molar ratio) of 95.2/4.8 and a weightaverage molecular weight of 470,000 was mixed at a mass ratio of 1:1.

This mixture was dissolved in a mixed solvent of dimethylacetamide andtripropylene glycol (dimethylacetamide/tripropylene glycol=8/2 [massratio]) to a concentration of 5% by mass to manufacture a coating liquidfor forming adhesive porous layer.

Equal amounts of the obtained coating liquid for forming adhesive porouslayer were coated on the both sides of the stacked body and theresultant was immersed in a coagulating liquid(water/dimethylacetamide/tripropylene glycol=57/30/13 [mass ratio]) at40° C. to solidify the coating liquid. The resultant was then washedwith water and dried.

By these operations, a separator including an adhesive porous layercomposed of PVDF-HFP was formed on one side of the polyethylenemicroporous membrane was obtained. Further, using the thus obtainedseparator, a test battery was manufactured by the same manner as inExample 101.

Example 202

A separator was obtained by the same manner as in Example 201 exceptthat the mass ratio of the filler, resin particles and CMC in thecoating liquid for forming heat resistant porous layer was changed to94.0/5.0/1.0. Further, using the thus obtained separator, a test batterywas manufactured by the same manner as in Example 101.

Example 203

A separator was obtained by the same manner as in Example 201 exceptthat a PVDF resin emulsion (KYNAR AQUATEC (registered trademark)manufactured by Arkema Inc.) was further added to the coating liquid forforming heat resistant porous layer, and the mass ratio of the filler,resin particles, KYNAR AQUATEC (registered trademark) and CMC in thecoating liquid for forming heat resistant porous layer was changed to81.0/9.0/9.0 (solid content)/1.0. Further, using the thus obtainedseparator, a test battery was manufactured by the same manner as inExample 101.

Example 204

A separator was obtained by the same manner as in Example 201 exceptthat the mass ratio of the filler, resin particles and CMC in thecoating liquid for forming heat resistant porous layer was changed to78.0/20.0/2.0. Further, using the thus obtained separator, a testbattery was manufactured by the same manner as in Example 101.

The characteristics and evaluation results of the separators and thetest batteries of Examples 201 to 204 are shown in Table 5 and Table 6.

TABLE 5 Heal resistant porous layer Adhesive porous layer Amount Ratioof Amount of of coated filler to CPVC coated liquid all of Thicknessliquid Provided Thickness (dry weight) materials filler Porosity Vf Vf/Provided (total) (dry weight) Porosity on [μm] [g/m²] [mass % ] [vol %][%] [vol %] CPVC on [um] [g/m²] [%] Example one side 2.3 2.4 96 43 5442.6 0.99 both sides 2 2.0 48 201 Example one side 2.4 2.4 94 43 53 40.00.93 both sides 2 2.0 48 202 Example one side 2.3 2.2 81 43 65 33.0 0.77both sides 2 2.0 48 203 Example one side 2.2 2.4 78 43 47 36.2 0.84 bothsides 2 2.0 48 204

TABLE 6 Average Weight porosity Thermal per of Film dimensional Shortunit coating Gurley resistance change Peel Handling Adhesion circuitCycles area layer value (1) [%] strength properties Slit to testcharacteristics [g/m²] [%] [sec/100 cc] [ohm · cm²] MD TD [N/cm] (2)properties electrode (2) [%] Example 12.4 51.2 236 4.30 0.1 0.1 0.12 A AA AA 89 201 Example 12.4 50.7 240 4.40 0.1 0.1 0.15 A A A AA 88 202Example 12.2 57.1 250 4.90 0.4 0.2 0.16 A A A AA 81 201 Example 12.447.5 387 6.48 0.7 1.2 0.16 A A A A 72 204

From the results shown in Table 6, it can be seen that the separators ofExamples 201 to 204 are excellent in ion permeability and thermaldimensional stability, and that the test batteries manufactured by usingthe separators of Examples 201 to 204 are excellent in batterycharacteristics and safety.

The disclosure of Japanese Patent Application No. 2012-262515 filed onNov. 30, 2012, Japanese Patent Application No. 2012-262516 filed on Nov.30, 2012, Japanese Patent Application No. 2013-056710 filed on Mar. 19,2013, Japanese Patent Application No. 2013-056712 filed on Mar. 19, 2013and Japanese Patent Application No. 2013-123873 filed on Jun. 12, 2013is incorporated by reference herein in its entirety.

All publications, patent applications, and technical standards mentionedin this specification are herein incorporated by reference to the sameextent as if such individual publication, patent application, ortechnical standard was specifically and individually indicated to beincorporated by reference.

The invention claimed is:
 1. A separator for a non-aqueous secondary battery, comprising: a porous substrate, and a heat resistant porous layer that is provided on one side or both sides of the porous substrate, that is an aggregate of resin particles and an inorganic filler, and that satisfies the following expression (1): 0.65≤Vf/CPVC≤0.99  expression (1) wherein, in expression (1), Vf is a volume proportion (% by volume) of the inorganic filler in the heat resistant porous layer, and CPVC is a critical pigment volume concentration (% by volume) of the inorganic filler, wherein the aggregate of resin particles is configured that plural resin particles and plural filler particles are joined to form the aggregate in a layer form, and the aggregate is fixed on the surface of the porous substrate via at least part of the resin particles, the resin particles include a resin selected from the group consisting of a polyvinylidene fluoride resin, fluoro rubber, styrene-butadiene rubber, ethylene-acrylate copolymer, ethylene-acrylic acid copolymer, polyethylene, ethylene-vinyl acetate copolymer, and a cross-linked acrylic resin, and the inorganic filler accounts for 50% by mass or more and less than 90% by mass of the total amount of the resin particles and the inorganic filler in the heat resistant porous layer.
 2. The separator for a non-aqueous secondary battery according to claim 1, wherein the heat resistant porous layer has a porosity of from 40% to 70%.
 3. The separator for a non-aqueous secondary battery according to claim 2, wherein a product obtained by multiplying the value of the porosity of the heat resistant porous layer by the value of Vf/CPVC is from 40% to 60%.
 4. The separator for a non-aqueous secondary battery according to claim 1, wherein a content of the inorganic filler in the heat resistant porous layer is from 2.0 g/m² to 20.0 g/m².
 5. The separator for a non-aqueous secondary battery according to claim 1, wherein the critical pigment volume concentration of the inorganic filler is from 20% by volume to 70% by volume.
 6. The separator for a non-aqueous secondary battery according to claim 1, wherein: the porous substrate includes a thermoplastic resin, and in a case in which the separator for a non-aqueous secondary battery is heated at a rate of temperature increase of 5° C./min. to a flow elongation deformation temperature of the thermoplastic resin, the separator for a non-aqueous secondary battery exhibits a thermal dimensional change ratio in a longitudinal direction of 3% or less and a thermal dimensional change ratio in a width direction of 3% or less.
 7. The separator for a non-aqueous secondary battery according to claim 1, wherein, in a case in which the separator for a non-aqueous secondary battery is subjected to a heat treatment at 150° C. for 30 minutes, the separator for a non-aqueous secondary battery exhibits a thermal shrinkage ratio in a longitudinal direction of 3% or less and a thermal shrinkage ratio in a width direction of 3% or less.
 8. The separator for a non-aqueous secondary battery according to claim 1, wherein the resin particles include a polyvinylidene fluoride resin.
 9. The separator for a non-aqueous secondary battery according to claim 1, wherein the inorganic filler is magnesium hydroxide or magnesium oxide.
 10. The separator for a non-aqueous secondary battery according to claim 1, wherein the heat resistant porous layer further comprises a thickener.
 11. A non-aqueous secondary battery comprising: a positive electrode, a negative electrode, and the separator for a non-aqueous secondary battery according to claim 1, which is disposed between the positive electrode and the negative electrode, wherein, in the non-aqueous secondary battery, an electromotive force is obtained by lithium doping/dedoping.
 12. The separator for a non-aqueous secondary battery according to claim 1, wherein the critical pigment volume concentration of the inorganic filler is from 20% by volume to 70% by volume, the inorganic filler is selected from the group consisting of magnesium hydroxide, alumina, magnesium oxide, aluminum hydroxide, kaolin, talc, plate boehmite, and plate calcium carbonate, and the resin particles include a polyvinylidene fluoride resin.
 13. The separator for a non-aqueous secondary battery according to claim 1, wherein the critical pigment volume concentration of the inorganic filler is from 20% by volume to 70% by volume, the inorganic filler is magnesium hydroxide, and the resin particles include a polyvinylidene fluoride resin.
 14. The separator for a non-aqueous secondary battery according to claim 1, wherein the inorganic filler accounts for 50% by mass or more and less than or equal to 86% by mass of the total amount of the resin particles and the inorganic filler in the heat resistant porous layer.
 15. The separator for a non-aqueous secondary battery according to claim 1, wherein the inorganic filler accounts for 50% by mass or more and less than or equal to 80% by mass of the total amount of the resin particles and the inorganic filler in the heat resistant porous layer. 